WO2002032163A2

WO2002032163A2 - Method of operating an asymmetrical half-duplex communication system

Info

Publication number: WO2002032163A2
Application number: PCT/US2001/029829
Authority: WO
Inventors: Paul Dent
Original assignee: Ericsson Inc.
Priority date: 2000-10-06
Filing date: 2001-09-24
Publication date: 2002-04-18
Also published as: AU2001293020A1; EP1325654A2; WO2002032163A3; JP2004511981A

Abstract

A mobile communications system is operated in a manner to improve its cpacity under the condition of asymmetric traffic flow. When similar amounts of traffic flow occur in each of downlink and uplink directions, channels in a first frequency band of a wireless spectrum are used to transmit information in the downlink direction from network stations to mobile terminals and channels in a second frequency band are used to transmit information in the uplink direction from mobile terminals to the network stations. Upon occurrence of asymmetric traffic flow as a result of themobile terminals receiving in total more information from than they transmit to the network stations, a division of the wireless spectrum into asymmetric uplink and downlink spectrums is made proportionally to the ratio of total uplink data flow to downlink data flow.

Description

METHOD OF OPERATING AN ASYMMETRICAL

HALF-DUPLEX COMMUNICAT8ON SYSTEM

Background of the Invention

The invention relates to wireless radio devices, such as mobile terminals, for receiving data at a higher data rate than they transmit data.

U.S. Patent No. 5,539,730, issued July 23, 1996 to the present inventor and entitled "TDMA/F DMA/CD MA Hybrid Radio Access Methods," describes asymmetrical communications systems that may employ different channel spacing and time slot durations in each direction of data transmission when the traffic flow in each direction in bits per second is the same, as in voice telephone calls. Equal traffic flow in both directions is therein achieved by ensuring that the product of the time slot duration and the channel bandwidth or data rate is the same in both directions. The teachings of said Patent No. 5,539,730 are specifically incorporated herein by reference.

More recently, increasing use of Internet, e-mail and IP-voice over the same Internet backbone exhibits an asymmetrical net flow of data between subscribers on the one hand and servers on the other hand. A server is typically a larger and more expensive computer having enormous storage space and multiple simultaneous input/output (I/O) capability, as compared to a subscriber terminal that may be a handheld device. The introduction of portable wireless subscriber terminals as a further development of mobile terminals or phones draws the wireless interface across the connections between mobile subscriber terminals and predominantly fixed servers, thereby creating an asymmetrical net traffic flow in the two directions across the wireless interface. This asymmetrical net traffic flow is not evident in the fixed network, as servers exhibit the opposite asymmetry to subscriber terminals, making the traffic flow in total symmetrical. The asymmetry for the wireless connection can be seen to be due to the relative absence of mobile servers, as they are not so portable as handheld devices.

There is a need to maximize the use of otherwise unused uplink capacity with the increasing trend to asymmetrical traffic flow across the wireless interface between mobile terminals and network servers.

Summary of the Invention

The invention meets this and other needs by providing a subscriber mobile terminal for accessing the Internet while on the move, and a wireless Internet server network in communication with a plurality of mobile terminals. When, as is typical, the mobile terminals in total receive more data from the network servers or base stations than they transmit in reply, a division of the wireless spectrum into uplink spectrum and downlink spectrum is made proportionally to the ratio of total uplink data flow to downlink data flow.

In one implementation of the invention, an amount of downlink spectrum (relative to a mobile terminal) is allocated for communication in the direction network station to mobile terminal while a lesser amount of uplink spectrum is allocated for communication in the direction mobile terminal to network station, such that the allocated amounts of uplink and downlink spectrum are in proportion to the total data traffic in the respective uplink and downlink directions.

A further implementation of the invention may be used where already allocated spectrum does not lend itself to being divided into a downlink band and an unequal uplink band while preserving adequate frequency spacing between any uplink channel and any downlink channel. Without such spacing, a mobile terminal transmitting in the same cell and adjacent in position and frequency to a receiving mobile terminal can cause unacceptable interference. Therefore, in this implementation the entire allocated spectrum is used for the downlink for a first portion of a repetitive frame period and for the uplink for a second portion of the frame period, the first and second portions of the frame period being in the ratio of the total downlink to total uplink traffic.

Brief Description of the Drawings

Fig. 1 illustrates a prior art asymmetrical TDMA format;

Fig. 2 shows, in accordance with one embodiment of the present invention, achieving unequal data rates on the uplink and downlink and a commensurate division of the total amount of frequency spectrum;

Fig. 3 shows a frequency/time utilization diagram for another embodiment of the invention;

Fig. 4 shows a further embodiment of the invention in which uplink and downlink transmission periods are interleaved;

Fig. 5 shows a 3-slot time reuse plan based on 3-sector cells;

Fig. 6 illustrates time reuse together with asymmetrical frequency allocations in uplink/downlink transmissions in accordance with still another embodiment of the invention; Fig. 7A illustrates time reuse, asymmetrical frequency allocations in uplink/downlink transmissions and staggered uplink/downlink channel timing slots in accordance with a further embodiment of the invention, and

Fig. 7B illustrates time reuse, asymmetrical frequency allocations in uplink/downlink transmissions and staggered uplink/downlink channel timing slots in accordance with a still further embodiment of the invention.

Detailed Description of the Invention

In accordance with the invention, the capacity for serving mobile terminals used in a mobile communications system is improved. This is accomplished by dividing the wireless spectrum into uplink and downlink generally proportional to ratio of uplink dataflow to downlink dataflow.

Fig. 1 illustrates a known asymmetrical TDMA (time-division multiple access) format according to above-incorporated Patent No. 5,539,730, in which there is equal traffic flow and equal capacity on the uplink and the downlink. A base or network station transmits sequentially in time slot 1 , time slot 2 and time slot 3, using a first downlink frequency band. A first mobile terminal 1 receives time slot 1 transmitted by the base station in an overlapping mobile terminal 1 receive time slot, and then transmits to the base station in a mobile terminal 1 transmit time slot which does not overlap in time with the mobile terminal 1 receive time slot, thereby avoiding the need for a transmit/receive duplexing filter at the mobile terminal. The mobile terminal 1 transmit time slot occupies a narrower bandwidth for a proportionally longer time than the corresponding base station transmit time slot 1 , while the time/bandwidth product is the same in both directions when the traffic flow rate in the two directions, i.e., in the uplink and downlink directions, is equal.

A base station transmit time slot 2 is used to transmit to another mobile terminal 2, which receives in an overlapping mobile terminal 2 receive time slot and then transmits to the base station in a mobile terminal 2 transmit time slot. In order for mobile terminal 2, mobile terminal 1 and indeed all mobile terminals to use the same terminal design and therefore the same transmit/receive timing, the receive/transmit timing of mobile terminal 2 is a delayed version of the receive/ transmit timing of mobile terminal 1 , i.e. the receive/transmit timing for mobile terminal 2 is advanced by the duration of one base station transmit time slot. Since this is less than the duration of the mobile terminal 1 transmit time slot, mobile terminal 1 is still transmitting when the mobile terminal 2 transmit time slot begins.

In order to allow the mobile terminal 1 and mobile terminal 2 transmit time slots to overlap in time, they are allocated different frequencies. Due to the narrower bandwidth of the mobile terminal transmit time slots, there are a proportionally greater number of frequencies available. Sequentially numbered mobile terminals access receive channel and time slot allocations as follows:

DOWNLINK DOWNLINK UPLINK UPLINK TIME SLO CHANNEL TIME SLOT CHANNEL

f1, t1 (t1+dt); f2, (t1+dt) - (t1+5dt)

f1, (t1+dt) - (t1+2dt) (f2+df), (t1+2dt) - (t1+6dt) f1, (t1+2dt) - (t1+3dt) (f2+2df), (t1+3dt) - (t1+7dt) f1, (t1+3dt) - (t1+4dt) (f2+3df), (t1+4dt) - (t1+8dt)

f1, (t1+4dt) - (t1+5dt) f2, (t1+5dt) - (t1+9dt)

f1, (t1+5dt) - (t1+6dt) (f2+df), (t1+6dt) - (t1+10dt)

f1, (t1+6dt) - (t1+7dt) (f2+2df), (t1+7dt) - (t1+11dt)

f1, (t1+7dt) - (t1+8dt) (f2+3df), (t1+8dt) - (t1+12dt)

f1, (t1+8dt) - (t1+9dt) f2, (t1+9dt) - (t1+13dt)

f1, (t1+9dt) - (t1+10d1 ); (f2+df), (t1+10dt) - (t1+14dt)

f1, (t1+10dt) - (t1+11d1 ); (f2+2df), (t1+11dt) - (t1+15dt)

f1, (t1+11dt) - (t1+12d1 ); (f2+3df), (t1+12dt) - (t1+16dt)

f1, (t1+12dt) - (t1+13d1 ); f2, (t1+13dt) - (t1+17dt)

f1, (t1+13dt) - (t1+14d1 ); (f2+df), (t1+14dt) - (t1+18dt)

f1, (t1+14dt) - (t1+15d1 ); (f2+2df), (t1+15dt) - (t1+19dt)

f1, (t1+15dt) - (t1+16d1 ); (f2+3df), (t1+16dt) - (t1+20dt)

For every downlink channel frequency fl of bandwidth 4df, there are four uplink channels starting at f2 of bandwidth df. The 16 time slots of duration dt illustrated above on the downlink channel fl have 16 corresponding uplink time slots of duration 4dt distributed as four time slots on each of the uplink channel frequencies. This asymmetrical TDMA system has equal traffic flow on the uplink and downlink, equal capacity on the uplink and downlink and the transmit/receive timing diagram is identical for every uplink/downlink channel pair.

The present invention is described herein in the context of a mobile terminal. As used herein, the term "mobile terminal" may include a mobile communications radiotelephone with or without a multi-line display; a Personal Communications System (PCS) terminal that may combine a mobile communications radiotelephone with data processing, facsimile and data communications capabilities; a PDA that can include a radiotelephone, pager, Internet/intranet access, Web browser, organizer, calendar and/or a global positioning system (GPS) receiver; and a conventional laptop and/or palmtop receiver or other appliance that includes a radiotelephone transceiver. Mobile terminals may also be referred to as "pervasive computing" devices.

While the invention is described relative to a TDMA system, the invention could also be used with other mobile communications systems, as will be apparent. Fig. 2 illustrates, in accordance with one embodiment of the invention, achieving unequal data rates on the uplink and downlink and a commensurate division of the total amount of spectrum between uplink and downlink. Three channels, Fdownl, Fdown2 and Fdown3, which are assigned different frequencies, are allocated to downlink transmissions in the network or base station to mobile terminal direction, and each channel is divided into eight time slots tl, t2 . . . t8. In this example, 3:1 asymmetry exists between downlink and uplink, and only one uplink channel frequency Fup is allocated for uplink transmissions in the base station to mobile terminal direction. The uplink frame is divided into 24 time slots t11-t13, t21 - 123, . . . t81 - 183, the indices respectively indicating to which of the eight downlink time slots and three downlink channels or frequencies each uplink time slot corresponds. The uplink time slots are 1/3 the duration of a downlink time slot, so to preserve like timing for all channels, every third uplink time slot is paired with an associated downlink time slot on a respective downlink channel frequency, and those in between uplink time slots are paired likewise with downlink time slots on other downlink channel frequencies. Moreover, the downlink time slot timing is staggered by one uplink time slot between different downlink frequency channels to preserve the same relative downlink/uplink time slot timing. The importance of providing the same downlink/uplink time slot timing for all network/mobile terminal links is to avoid protocol changes in such matters as whether a packet can be acknowledged immediately after it is received, with due allowance for any processing delays. If there were variable delays between uplink and downlink time slots, different links may be needed to use variations in the protocol to allow for processing delays, which is undesirable. The invention, on the other hand, advantageously maintains the same timing for all links, and it therefore is not necessary to adapt a packet protocol in dependence upon the exact frequency and time slot allocated.

Fig. 2 also illustrates how the uplink frequencies and time slots are arranged if a lower asymmetry of 3:2 exists between downlink and uplink, instead of an asymmetry of 3:1. In this case, two uplink frequencies, Fup1 and Fup2, are each divided into 12 time slots, with each time slot having twice the duration of the uplink Fup time slots for the above case where there is 3:1 asymmetry. The labeling of slots, t11 , t12 . . . etc., indicates the pairing of uplink slots and frequencies with downlink slots and frequencies for the case of an asymmetry of 3:2. In general, if there are N1 downlink carriers or channels and N2 uplink carriers or channels, then there are M1 downlink time slots per downlink carrier, of duration M1dt, and M2 uplink time slots per uplink carrier, of duration M2dt, such that M1 -N1=MZ-N2.

The embodiment of the invention illustrated by Fig. 2 may be used when the frequency band allocated to the downlink contains more spectrum than the frequency band allocated to the uplink. However, there must be a guard band between the downlink frequency bands and the uplink frequency band(s), so that a mobile terminal that is receiving on any downlink time slot, e.g., time slot t4 on channel Fdown3, is not interfered with by a simultaneous transmission from a nearby mobile terminal, e.g., in uplink slot t83 on Fup. If Fup and Fdown3 are not separated, but instead are adjacent channels, the mobile terminal transmitting on t83, in the same cell as the mobile terminal receiving on t4, can cause interference.

When the spectrum is already allocated symmetrically and does not meet the above requirements for asymmetrical allocation, then in accordance with another embodiment of the invention, all of the spectrum is alternately used for downlink transmissions for a first portion of a time period of a frame and then for uplink transmissions for a second portion of the time period of the frame. Fig. 3 shows a frequency/time utilization diagram for this embodiment. Conventionally, the frequency spectrum is divided into a first band (BAND 1) envisaged for the uplink direction of a symmetrical cellular system and a second band (BAND 2) envisaged for the downlink direction of the symmetrical cellular system. It is now, however, desired to divide the capacity available with these two frequency bands unequally between uplink and downlink traffic. Thus, this embodiment contemplates that each of BAND 1 and BAND 2 be used for downlink traffic transmission for a first and greater part of a frame period and for uplink traffic transmission for a second and lesser part of the frame period. As seen, the downlink frame period is 2/3 of the time period of a frame and is divided into eleven time slots. The uplink frame period is the remaining 1/3 of the time period

of the frame and also is divided into 1 1 time slots that are, therefore, half the duration of the downlink time slots.

A disadvantage of the Fig. 3 embodiment is that it is impossible to pair uplink time slots with downlink time slots in such a way that the uplink/downlink relative timing is the same for all links. For example, the spacing between

downlink time slot td1 and uplink time slot tu1 is 2/3 of a frame period, while the spacing between downlink time slot td1 1 and uplink time slot tu1 1 is 1/3rd of the frame period. Thus, a mobile terminal allocated the uplink and downlink time slots td1 , tu1 has 2/3 of the frame to process the data received in td1 and formulate a response in tu1 , while a mobile terminal allocated the uplink and downlink time

slots tu1 1 , td11 has only 1/3 of the frame period to receive, process and respond. The network station also experiences these differences in the opposite sense, and while a packet protocol may be used to handle such variable delays, it is difficult to design a packet protocol that would efficiently do so. This problem may overcome by interleaving the uplink and downlink time slots or transmission

periods, as shown in Fig. 4.

Fig. 4 shows division of the frame period into 1 1 units, each comprising an uplink time slot period and a downlink time slot period. Any particular uplink time slot need not immediately follow its corresponding or associated downlink time slot, which can involve practical difficulties in adapting the mobile terminal in short time from receive to transmit. Such difficulties can include synthesizer switching times, antenna changeover times and delay due to the finite speed of processing. This embodiment of the invention therefore contemplates that the uplink time slot tu1 for mobile terminal 1 be placed 5 time units away from the corresponding downlink time slot td1 for the mobile terminal, in the same time unit that contains downlink time slot tdδ. With this arrangement of uplink and downlink time slots, all links corresponding to time slot pairs (td1 , tu1), (td2, tu2) . . . (td11 , tu11) have the same relative timing of about half a frame period between receive and transmit. A guard time is required between each downlink time slot and the immediately following uplink time slot, as radar-type echoes of the network station's own transmission in a downlink time slot must be over before it attempts to receive from a mobile terminal. Because of such radar-type echoes, the above-described Fig. 3 embodiment has the additional disadvantage that a network base station may receive interference from other network base station transmissions that, although synchronized, were received late due to propagation delay. Since base stations have substantial antenna gain and height, a base station may receive signals from another base station, despite the base stations being separated by a great distance. Therefore, for outdoor, long-range systems having great disparity between mobile terminal powers and antenna gains, and corresponding base station powers and antenna gains, it is preferred to reserve a portion of the channels for base station transmission, and different channels for base station reception, as per the Fig. 2 embodiment of the invention. This problem may not exist, however, for indoor systems of similar base and mobile terminal powers and antenna gains.

For outdoor systems, a different solution is therefore required to prevent one mobile terminal transmission from interfering with another mobile terminal receiving in the same cell and to prevent one base station's transmission interfering with another's reception. It also is necessary to prevent interference between neighboring cells. For the latter purpose, the teachings of prior U. S. patents nos. 5,555,257, 5,594,941 , 5,619,503, 5,631 ,604, 5,812,947 and 5,848,060 may be utilized, all of which patents issued to the present applicant and the teachings of which are specifically incorporated herein by reference. These patents teach both frequency reuse and time reuse planning for ensuring there is at least a minimum distance between cells that use the same frequency at the same time. Time reuse as taught by said patents may be employed to alleviate the interference problems mentioned above.

Fig. 5 shows a 3-slot time reuse plan based on 3-sector cells. Sectorization is a common technique used in cellular systems to reduce the amount of real estate required for antenna sites by a factor of 3 or more. Instead of illuminating a cell from an antenna at its center, three neighboring cells are illuminated by a common antenna at their mutual boundary, the antenna having three, 120 degree directional patterns corresponding to the three cells, which are then renamed "sectors". When the three sectors of the same site use three different frequencies, but adjacent sites use the same three frequencies, such a frequency plan is termed a 1-site, 3-sector plan. With careful use of power control, coding and adaptive channel allocation to ensure that only three mobile terminals corresponding to the three different frequencies are served in regions of overlap where service to more than three mobile terminals can otherwise occur, such as those shown encircled in Fig. 5, the interference between sectors and sites may be minimized. Other techniques to minimize inter-site interference are described in said above-incorporated prior patents and other prior art. Such techniques include the use of more sectors,

known as interstitial sectors, as well as reuse partitioning in which sub-channels are used for mobile terminals lying at different radii from each antenna site, where

the association of sub-channels to radial distance is permuted between adjacent sites according to a regular pattern. In Fig. 5, different time-partitions of a frame period t1 , t2 and t3, instead of different frequency channels, have been used to form a reuse pattern.

Fig. 6 illustrates how a time reuse plan between neighboring cells or sectors can be used together with asymmetrical frequency allocations to the uplink and downlink traffic to avoid having one mobile terminal transmission interfere with another mobile terminal reception in the same cell in the same

frequency band. As before, it is assumed that cellular frequency allocations of a first BAND 1 and a second BAND 2 were already made with the assumption of symmetrical uplink and downlink traffic. To accommodate a maximum amount of asymmetric traffic, an amount of uplink spectrum is used for downlink traffic. However, to avoid interference to a mobile terminal that receives in the uplink spectrum from a nearby mobile terminal that is transmitting in the uplink spectrum, as shown in Fig. 6, a time reuse plan is implemented between the three sectors of a site, instead of the more conventional frequency reuse plan. In particular, the frame period shown on the horizontal time scale is divided into three regions: (1) a first region comprising 1/3 of the frame period, used on the uplink by sector 3, on the downlink by sector 1 and containing three downlink time slots TD1 , TD2 and TD3; (2) a second region comprising 1/3 of the frame period, used on the uplink by sector 1 , on the downlink by sector 2 and also containing three downlink time slots, and (3) a third region comprising 1/3 of the frame period, used on the uplink by sector 2, on the downlink by sector 3 and containing three downlink time slots. The frequency spectrum is shown, for simplicity, on the vertical scale as being divided into three downlink frequency channels Fdownl, Fdown2 and Fdown3, and one uplink channel Fup. Downlink frequency channel Fdownl lies in BAND 1 , the traditionally uplink part of the spectrum.

A mobile terminal in sector 1 that receives time slot TD1 on the downlink in frequency channel Fdownl transmits on an uplink time slot designated T11 on the uplink channel Fup, where in the uplink time slot T11 the indices respectively represent the downlink time slot and the downlink frequency of the corresponding mobile terminal in the associated sector. Since there are three downlink frequency channels and three downlink time slots in each sector, there are nine simultaneous links in each sector, each requiring a corresponding uplink. Therefore, the frame period of the uplink channel Fup has to be divided into 27 uplink time slots, nine for each sector. However, the nine uplink time slots for sector 1 have been shifted to that 1/3 of the frame period in which sector 2 mobile terminals are receiving, sector 2 uplink time slots are in the 1/3 of the frame period in which sector 3 mobile terminals are receiving, and sector 3 uplink time slots are in the 1/3 of the frame period when sector 1 mobile terminals are receiving. Thus, a mobile terminal receiving in the uplink spectrum (BAND 1 ) lies in a different sector than a mobile terminal transmitting in the uplink spectrum, which is sufficient spatial separation to avoid interference.

From Fig. 6 it is seen that the sector 1 uplink time slot T11 is approximately six uplink time slot durations away from the end of its corresponding downlink slot TD1. On the other hand, sector 1 uplink time slot T12, which corresponds to downlink slot TD1 on channel Fdown2, is seven uplink time slots away from its corresponding downlink time slot, and sector 1 time slot T13 is 8 time slots away from its corresponding downlink time slot. Sector 1 uplink time slot T21 is, again, six time slots away from the end of its corresponding downlink time slot TDZ on channel Fdownl, and so on for the remaining uplink time slots. There is thus a small variation in relative timing of between 6 and 8 uplink time slots between an uplink time slot and its corresponding previous downlink slot. This variation may be eliminated with the frequency-time diagrams as shown in Figs. 7A and 7B. In Fig. 7A, the time slot timing is successively staggered between downlink channels Fdown3, Fdown2 and Fdownl in steps of an uplink time slot width. Since downlink time slot TD3 on Fdownl now overlaps what in Fig. 6 was sector 1 's uplink time region, this would cause a problem since a mobile terminal receiving in TD3 in band 1 would overlap two other mobile terminals transmitting in the same band 1 and in the same sector on uplink time slots T11 and T12 on Fup. To avoid this, the uplink sector timing of Fig. 7A has been shifted one additional sector as compared to the uplink timing of Fig. 6. Alternatively, time-staggering of downlink time slots could be as in Fig. 7B, which does not shift the time slots on Fdownl relative to the uplink time slots. Nevertheless, with the same uplink sector timing

as in Fig. 6, downlink time slot TD3 on Fdown3 for sector 1 would overlap uplink time slots T1 1 and T12 (on Fup) for sector 1 , which may not cause interference, but prevents the allocation to one mobile terminal of a high data rate duplex link

that would use all three downlink time slots and all nine uplink time slots allocated to the sector. To preserve flexibility to allocate up to a whole sector's capacity to one mobile terminal, it is therefore desirable to shift the uplink sector time slot allocation as compared to Fig. 6, and such shifted sector timings are 5 illustrated in Fig. 7B. Moreover, for mobile terminals with wideband receivers covering BAND 1 and BAND 2, it is undesirable for a mobile terminal to transmit in a sector on any frequency at the same time as another mobile terminal is receiving in the same sector, as occurs even in Fig. 7B during downlink time slot TD3, which would overlap uplink time slots T1 1 ,T12 of the same sector if the sector timings of Fig. 6 had been retained. This is avoided with the additional one-sector uplink timing shift illustrated in Fig. 7B.

With the staggered downlink time slot timing of Figs. 7A or 7B, the relative timings between downlink time slots (such as TD l/Fdownl, TD1/Fdown2, TD

l/Fdown3) and their corresponding uplink time slots (T1 1 , T12, T13) are now all identical with a relative delay of 15 uplink time slots (5 downlink time slots) between the end of a downlink time slot and the start of the corresponding uplink

time slot.

The system illustrated by Fig. 7B is an exemplary embodiment of the invention and may be generalized, as above described, for cases where there are N1 downlink time slots and Ml frequency channels per sector, combined with N2 uplink time slots and M2 uplink frequency channels per sector, such that M1 ^»N1 =M2'N2. It also is possible to vary the partitioning of the capacity between the sectors, for example by labeling four of the 9 downlink slots (and their corresponding uplink slots) as belonging to sector 1 , while only two are allocated to sector 2 or to sector 3. As long as the non-interference criteria are met, this provides for flexible "soft capacity", by which is meant the ability to move capacity from an underloaded sector or cell to where it is instantaneously needed in a heavily loaded cell.

Thus, according to the teachings of the invention cellular systems are optimized for asymmetric traffic flow, by transferring a portion of traditionally uplink spectrum to downlink use. A portion of the uplink and downlink band are optimized for traffic flow in this manner, leaving another portion for traditional symmetric traffic, so long as interference from mobile terminals transmitting in the symmetric traffic manner are not permitted to interfere with mobile terminals receiving in the new asymmetric traffic manner or vice-versa.

While embodiments of the invention have been described in detail, one skilled in the art thereof may devise various modifications and other embodiments without departing from the spirit and scope of the invention, as defined by the appended claims. For example, using the above teachings, a person skilled in the art may devise many variations of the invention, including frequency or time reuse patterns other than the 3-sector, 1-site plan discussed and illustrated above for the purpose of teaching the principals of the invention. Such variations fall within the scope and spirit of the invention.

Claims

CLAIMS I Claim:

1. A method of adapting a mobile communications system to improve capacity of the system for handling asymmetric traffic flow, comprising: using channels in a first frequency band for transmitting information in a direction from network stations to mobile terminals, and channels in a second frequency band for transmitting information in a direction from mobile terminals to network stations, when rate of information transmission in the two directions is similar; and using other channels in the second frequency band for transmitting information from network stations to mobile terminals when the rate of information transmission in the two directions is dissimilar.

2. A method of improving capacity of a mobile system to handle asymmetric traffic flow, comprising: allocating a first number N1 of channels for transmitting information from network stations to mobile terminals and a second number N2 of channels for transmitting information from mobile terminals to network stations, a ratio of the first number of channels to the second number of channels being determined by a ratio of amount of information to be transmitted in the respective directions; dividing a repetitive frame period into a first number M1 of time slots for the first number of channels and into a second number M2 of time slots for the second number of channels, such that M1-N1=M2-N2 ; and allocating to each mobile terminal an associated one of the first number of channels and one of the first number of time slots of the channel for transmitting information from network stations to mobile terminals, and allocating to each mobile terminal a corresponding one of the second number of channels and one

of the second number of time slots of the channel for transmitting information from mobile terminals to the network stations.

3. The method of claim 2, wherein each one of the first number of time slots is spaced by a fixed amount of time from a corresponding one of the second number of time slots.

4. The method of claim 2, wherein the first number of time slots on different ones of the first number of channels have relatively staggered timing in predetermined steps of time offset.

5. The method of claim 4, wherein the second number of time slots on different ones of the second number of channels have relatively staggered timing

in the same predetermined steps of time offset.

6. A method of improving capacity of a mobile system to handle asymmetric traffic flow, comprising: using a first frequency band for transmissions from network stations to mobile terminals and a second frequency band for transmissions from mobile terminals to network stations when traffic flow is generally symmetric; and when traffic flow is asymmetric, dividing a repetitive frame period of the frequency bands into a first portion of time used for transmission in the direction from network stations to mobile terminals and into a second portion of time used for transmission in the direction from mobile terminals to network stations, the first and second portions of time being in the ratio of the traffic flow in respective directions.

7. The method of claim 6, further comprising transmitting traffic from at least one of the network stations to at least one of the mobile terminals using the second frequency band in the first portion of time.

8. The method of claim 6, further comprising dividing the first portion of time into a number of time slots and the second portion of time into the same number of time slots, and allocating to each mobile terminal an associated time slot in the first portion of time and a corresponding time slot in the second portion of time for the network stations to communicate with each one of the mobile terminals and for the mobile terminals to communicate with the network stations.

9. The method of claim 8, wherein the time slots of the second portion of time are contiguous time slots.

10. The method of claim 8, wherein the time slots of the first portion of time are contiguous time slots.

11. The method of claim 8, wherein each time slot of the second portion of time lies between two time slots of the first portion of time.

12. A method of adapting a mobile system between symmetric and asymmetric traffic flow, comprising: using a first frequency band for transmissions from network stations to mobile terminals and a second frequency band for transmissions from mobile terminals to network stations when traffic flow is symmetric; and when traffic flow is asymmetric, dividing the first and second frequency bands jointly into a first number N1 of frequency channels for transmitting information from network stations to mobile terminals and a second number N2 of frequency channels transmitting information from mobile terminals to network stations, the first and second numbers being in a ratio related to the amount of information to be transmitted in respective directions.

13. The method of claim 12, further comprising: dividing a repetitive frame period into a first number M1 of time slots for the first number N1 of channels and into a second number M2 of time slots for the second number N2 of channels, such that M1 *N1=M2^»N2.

14. The method of claim 13, further comprising: allocating to each mobile terminal an associated one of the first number of channels and one of the first number of time slots of the channel for transmitting information from network stations to mobile terminals, and allocating to each mobile terminal a corresponding one of the second number of channels and one of the second number of time slots of the channel for transmitting information from mobile terminals to the network stations.

15. The method of claim 14, wherein each one of the first number of time slots is spaced by a fixed amount of time from the corresponding one of the second number of time slots.

16. The method of claim 15, wherein the first number of time slots on different ones of the first number of channels have relatively staggered timing in predetermined steps of time offset.

17. The method of claim 16, wherein the second number of time slots on different ones of the second number of channels have relatively staggered timing in the same predetermined steps of time offset.

18. The method of claim 12, further comprising: dividing a repetitive frame period into different portions of time used for transmission in different neighboring geographical regions, and assigning individual portions of the first and second numbers of channels to associated ones of the portions of time of the frame period to avoid interference between neighboring geographical regions.

19. The method of claim 18, wherein transmission in the direction from mobile terminal to network station occurs in any one of the neighboring

geographical regions in the portion of time used for transmission in the direction from network station to mobile terminal in a different one of the geographical regions.

20. The method of claim 18, wherein the portions of time used for transmission in the direction mobile terminal to network station are time-staggered relative to the portions of time used for transmission in the direction network station to mobile terminal

21 . The method of claim 18, wherein the geographical regions are the angular sectors served by a sectorized network station directional antenna.

22. The method of claim 21 , wherein the different portions of time are unequal and are adapted proportionally to the traffic load in respective sectors.

23. A method of adapting a mobile communications system to increase capacity of the system upon occurrence of asymmetric traffic flow, comprising: using channels in a first frequency band of a wireless spectrum to transmit information in a downlink direction from a network station to mobile terminals and channels in a second frequency band of the wireless spectrum to transmit information in an uplink direction from said mobile terminals to said network station, when amounts of information transmitted in the uplink and downlink directions are similar; and when the amounts of information transmitted in the uplink and downlink directions are asymmetric, alternately employing the wireless spectrum solely for downlink transmission of information from said network station to said mobile terminals for a first portion of a time period of a repetitive frame and then solely for uplink transmission of information from said mobile terminals to said network station for a second portion of the time period of the frame.

24. The method of claim 23, wherein the duration of the first portion of a time period of a frame to the second portion of the time period of the frame is related to the ratio of the amounts of information transmitted in the respective downlink and uplink directions.

25. The method of claim 23, comprising: simultaneously using each of the first and second frequency bands for the downlink and uplink transmission of information.

26. The method of claim 23, comprising: using the first frequency band to serve some of the mobile terminals for uplink and downlink transmissions and the second frequency band to serve the remaining mobile terminals for uplink and downlink transmissions.

27. The method of claim 24, comprising: dividing the first portion of the time period of a frame into a number M1 of downlink time slots of equal duration for downlink transmission of information from said network stations to associated ones of the mobile terminals and the second portion of the time period of the frame into a number M2 of uplink time slots for uplink transmission of information from associated ones of the mobile terminals to said network station, wherein M1 equals M2 and the duration of the downlink time slots to the duration of the uplink time slots is related to the ratio of amounts of traffic transmitted in the respective downlink and uplink directions.

28. The method as in claim 27, comprising: causing all of the downlink time slots to occur together in each frame and then all of the uplink time slots to occur together in each frame.

29. The method of claim 27, comprising: causing the downlink and uplink time slots to occur alternately in the frame, such that an uplink and a downlink time slot occur consecutively and form a time-unit of constant duration equal to the sum of a downlink and an uplink time slot duration.

30. The method of claim 29, comprising: causing the downlink time slot of a first time-unit to be paired with the uplink time slot of a second time-unit spaced by a fixed number of time-units from the first time-unit so as to form an uplink/downlink time slot-pair for a given network station/mobile terminal link and to maintain the same uplink/downlink relative time slot timing for each link.

31. A method of operating a cellular system to increase capacity of the system upon occurrence of asymmetric traffic flow in a wireless spectrum used by the cellular system, the asymmetric traffic flow occurring when a greater amount of information is transmitted in a downlink direction from network stations to mobile terminals than is transmitted in an uplink direction from mobile terminals to network stations, comprising: upon occurrence of asymmetric traffic flow, allocating a greater portion of the wireless spectrum for use by downlink traffic than by uplink traffic.

32. The method of claim 31 , wherein allocating a greater portion of the wireless spectrum for use by downlink traffic than by uplink traffic comprises separating the wireless spectrum into a first number N1 of frequency channels for transmitting information in the downlink direction from network stations to mobile terminals and a second number N2 of frequency channels for transmitting information in an uplink direction from mobile terminals to network stations, the ratio of the first and second numbers Nl and N2 of channels being determined by the ratio of the amounts of information to be transmitted in the respective downlink and uplink directions;

33. The method of claim 32, comprising: dividing a repetitive frame period for each of the first and second numbers N1 and N2 of channels into a first number Ml of downlink time slots for the first number Nl of channels and into a second number M2 of uplink time slots for the second number N2 of channels, such that MI*NI=MZ*N2; and allocating to each one of the mobile terminals an associated one of the first number N1 of channels and one-of the downlink time slots of the channel for transmitting information from one of the network stations to the mobile terminal, and also allocating to each one of the mobile terminals a corresponding one of the second number N2 of channels and one of the uplink time slots of the channel for transmitting information from the mobile terminal to the one network station.

34. The method of claim 33, wherein each one of the first number M1 of downlink time slots is spaced by a fixed amount of time from a corresponding one of the second number M2 of uplink time slots.

35. The method of claim 33, wherein the downlink time slots of each of the first number Nl of channels have relatively staggered timing, in predetermined steps of time offset, with respect to the downlink time slots of each of the other channels of the first number.

36. The method of claim 35, wherein the uplink time slots of each of the

plurality of the second number N2 of channels have relatively staggered timing in the same predetermined steps of time offset.

37. A method of operating a cellular system to increase capacity of the system upon occurrence of asymmetric traffic flow in a wireless spectrum used for transmission by the cellular system, comprising: using a first frequency band of the wireless spectrum for downlink transmissions from network stations to mobile terminals and a second frequency band of the wireless spectrum for uplink transmissions from mobile terminals to network stations when traffic flow in uplink and downlink directions is generally

symmetric; and allocating a portion of the second frequency band of the wireless spectrum for downlink transmissions from network stations to mobile terminals upon occurrence of asymmetric traffic flow, which occurs as a result of a greater amount of information being transmitted in a downlink direction from network stations to mobile terminals than in an uplink direction from mobile terminals to

network stations.

38. A method of operating a cellular system to increase capacity of the system upon occurrence of asymmetric traffic flow in a wireless spectrum used by the cellular system, which occurs as a result of a greater amount of information

being transmitted in a downlink direction from network stations to mobile terminals than in an uplink direction from mobile terminals to network stations, comprising: using a first frequency band of the wireless spectrum for downlink transmissions from network stations to mobile terminals and a second frequency band of the wireless spectrum for uplink transmissions from mobile terminals to network stations when traffic flow in uplink and downlink directions is generally symmetric; and upon occurrence of asymmetric traffic flow, dividing the wireless spectrum into first and second portions used for respective downlink and uplink transmissions, wherein the first and second portions are in the ratio of the information to be transmitted in the respective downlink and uplink directions.

39. The method of claim 38, wherein dividing the wireless spectrum into first and second portions for respective downlink and uplink transmissions comprises: dividing a repetitive frame period into first and second portions of time in one of the frequency bands, wherein the first and second portions of time have durations corresponding to the ratio of the information to be transmitted in the respective downlink and uplink directions, and using the first portion of time in the one frequency band for downlink transmission from network stations to mobile terminals and the second portion of time for uplink transmission from mobile terminals to network stations.

40. The method of claim 39, further comprising:

dividing the first portion of time into a number M1 of downlink time slots and the second portion of time into a number M2 of uplink time slots, such that

M1 =M2, and allocating to each mobile terminal an associated one of the downlink time

slots in the first portion of time and a corresponding one of the uplink time slots in the second portion of time for use in the transmission of information between the network stations and the mobile terminals.

41 . The method of claim 40, wherein the downlink time slots in the first portion of time are contiguous.

42. The method of claim 40, wherein the uplink time slots in the second portion of time are contiguous.

43. The method of claim 40, wherein each of the uplink time slots lies

between two of the downlink time slots, such that the downlink and uplink time

slots occur alternately in the frame.

44. A method of adapting a mobile system between symmetric and

asymmetric traffic flow, comprising: using a first frequency band of a wireless spectrum for downlink transmissions from network stations to mobile terminals and a second frequency band of the wireless spectrum for uplink transmissions from mobile terminals to network stations when traffic flow in the downlink and uplink directions is generally symmetric; upon occurrence of asymmetric traffic flow in the wireless spectrum, which occurs as a result of a greater amount of information being transmitted in the downlink direction from network stations to mobile terminals than in the uplink direction from mobile terminals to network stations, allocating at least a portion of the second frequency band for downlink transmissions from network stations to mobile terminals.

45. The method of claim 44, wherein allocating at least a portion of the second frequency band for downlink transmissions from network stations to mobile terminals comprises dividing the first and second frequency bands jointly into a first number N1 of frequency channels for downlink transmissions from network stations to mobile terminals and a second number N2 of frequency channels for uplink transmissions from mobile terminals to network stations, the first and second numbers N1 and N2 being in the ratio of the amount of information to be transmitted in respective downlink and uplink directions.

46. The method of claim 45, further comprising dividing a repetitive frame period for each of the first and second numbers N1 and N2 of frequency channels into a first number Ml of downlink time slots for the first number N1 of downlink channels and into a second number M2 of uplink time slots for the second number N2 of uplink channels, such that Ml -NI=M2-N2.

47. The method of claim 46, further comprising allocating to each mobile terminal that is to communicate with a network station an associated downlink frequency channel and downlink time slot of the channel and an associated uplink frequency channel and uplink time slot of the channel, for downlink and uplink

transmission of information between the mobile terminal and the network terminal.

48. The method of claim 47, wherein each of the downlink time slots is spaced by a fixed amount of time from a corresponding one of the uplink time slots.

49. The method of claim 48, wherein the downlink time slots of each of the downlink channels have relatively staggered timing in predetermined steps of time offset with respect to the downlink time slots of other downlink channels.

50. The method of claim 49, wherein the uplink time slots of each of the uplink channels have relatively staggered timing in the same predetermined steps

of time offset.

51. A mobile communications system adapted to improve capacity of the system for handling asymmetric traffic flow, comprising: a network station for transmitting information in a downlink direction using

channels in a first frequency band; and a plurality of mobile terminals for transmitting information in an uplink direction from mobile terminals to network stations using channels in a second frequency band when a rate of information transmission in the two directions is similar, wherein the network station uses other channels in the second frequency band for transmitting information in a downlink direction to mobile terminals when the rate of information transmission in the two directions is dissimilar.

52. The mobile communications system of claim 51 wherein, when the rate of information transmission in the two directions is dissimilar, the first and second frequency bands are divided jointly into a first number N1 of frequency channels for transmitting information in the downlink direction and a second number N2 of frequency channels transmitting information in the uplink direction, the first and second numbers being in the ratio of the amount of information to be transmitted in the respective directions.

53. The mobile communications system of claim 52 wherein a repetitive frame period is divided into a first number M1 of time slots for the first number N1 of channels and into a second number M2 of time slots for the second number N2 of channels, such that M1 ^«N1 =M2^«N2.

54. A mobile communications system adapted to improve capacity of the system 2 for handling asymmetric traffic flow, comprising: a network station for transmitting information in a downlink direction; and a plurality of mobile terminals for transmitting information in an uplink direction,

wherein a first number N1 of channels are allocated for transmitting information in the downlink direction and a second number N2 of channels are

allocated for transmitting information in the uplink direction, a ratio of the first number of channels to the second number of channels being determined by a ratio of amount of information to be transmitted in the respective directions, a repetitive frame period is divided into a first number M1 of time slots for the first number of channels and into a second number M2 of time slots for the second

number of channels, such that M1 -N1=M2-N2 , and each mobile terminal is allocated an associated one of the first number of channels and one of the first number of time slots of the channel for transmitting information in the downlink direction, and each mobile terminal is allocated a corresponding one of the second number of channels and one of the second number of time slots of the channel for transmitting information in the uplink direction.

55. The mobile communications system of claim 54, wherein each one of the first number of time slots is spaced by a fixed amount of time from a corresponding one of the second number of time slots.

56. The mobile communications system of claim 54, wherein the first

number of time slots on different ones of the first number of channels have relatively staggered timing in predetermined steps of time offset.

57. The mobile communications system of claim 56, wherein the second number of time slots on different ones of the second number of channels have relatively staggered timing in the same predetermined steps of time offset.