AU2316601A - Cellular radio communication system with a channel quality criterion - Google Patents

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant/s: Actual Inventor/s: Address for Service: Invention Title: Stanford Telecommunications, Inc Aki Shohara BALDWIN SHELSTON WATERS 60 MARGARET STREET SYDNEY NSW 2000 'CELLULAR RADIO COMMUNICATION SYSTEM WITH A CHANNEL QUALITY CRITERION' Details of Original Application No. 14083/97 dated 11 December 1996 The following statement is a full description of this invention, including the best method of performing it known to me/us:- File: 30859AUP00 -la- CELLULAR RADIO COMMUNICATION SYSTEM WITH A CHANNEL QUALITY CRITERION Background of the Invention The invention is in the class of terrestrial cellular digital radio systems that provide demand assignment multiple access (DAMA) conmmunications service to subscriber terminals equipped with narrowbeam radio antennas. Thus, the subject class of cellular radio systems has a set of terrestrial radio base stations distributed over the service area, where each base station is equipped with sector antennas, and each sector antenna has associated transmitter/receivers that communicate via frequency division multiplexed (FDM) radio wave with subscriber terminals in the vicinity of the base station.

Communications is two-way with radio wave transmission in the direction from base station to terminal termed the downlink direction, and in the direction from terminal to base station termed the uplink direction. Each subscriber terminal, has a narrow beam antenna that is pointed into the aperture of one of the base station sector antennas assigned to the terminal. The terminal antenna has an associated transmitter and a receiver tunable to assigned sector FDM channels. The channel assignment originates in 20 a service center on a DAMA basis.

-2- The FCC allocates a block of radio spectrum for specified terrestrial cellular radio services. The radio frequency band allocated to a cellular radio system is a precious natural resource, and it is of utmost concern to national and international regulatory agencies that the allocated radio spectra be efficiently used. For the cellular radio service providers increased spectral utilization efficiency implies reduction of the density of base stations required to cover a given service area. The resultant reduction of infrastructure cost may then result in reduction of service cost to subscribers. Thus, the realization of increased spectral utilization efficiency of cellular radio systems, which is an objective of the preferred embodiment of the invention has important economic and social benefits. Cellular radio systems employ frequency reuse of the block of spectra allocated to the cellular system in order to achieve high spectral efficiencies. Typically the allocated block is partitioned into two parts, one part for radio wave transmission from base stations to the subscriber terminals, hereafter defined to be the uplink 15 direction, and the other part for radio wave transmission from terminals to base stations, hereafter defined to be the uplink direction. The uplink part is further partitioned into frequence-division multiplexed (FDM) channels, and the channels are partitioned into N groups of channels Fl, F2, FN, where the number N is defined as the frequency reuse number. Each sector antenna of the cellular system is allocated one of the channel groups in such a way that *aaaa.

a. o a a o 3 for large numbers of sectors, the frequencies are reused. All sectors assigned the same channel group are termed co-channel sectors. A natural consequence of frequency reuse in cellular radio systems is that transmissions in the channel of one sector have the potential to interfere with transmissions in nearby cochannel sector and such interference is termed co-channel interference. Cellular systems utilize frequency allocation patterns that approximate idealized regular patterns known to have minimal co-channel interference levels for a given frequency reuse number N. The level of co-channel interference in a channel is defined in this disclosure as significant if it causes the channel to fail a defined channel quality criterion such as bit error rate.

In this disclosure spectral efficiency is defined as E MP/N where M is the number of sectors per cell in a cellular pattern, and N is the number of channel groups. The efficiency o thus equals the number of times the allocated frequencies are reused at each base station. The factor P is accounts for 20 polarization usage and is generally equal to one. In the special case when both polarizations of a channel group are allocated to ooe a sector, then P 2. For fixed base station complexity (M fixed) in general, reduction of the frequency reuse number N in an attempt to increase efficiency tends to generally increase the level of co-channel interference in the system so that there exists a fundamental tradeoff of spectral efficiency with the ooooo .a 4level of co-channel interference present in the network.

Conventional DAMA channel assignment algorithms associated with prior art typically treat all terminals uniformly without attempting to ascertain the co-channel interference characteristics of the terminal. A drawback to the conventional approach is that in order to guard against the random occurrence of unexpectedly large co-channel interference in assigned channels the use of spectrally inefficient cellular patterns with large reuse number N is needed, particularly when a guaranteed channel quality criterion is required by terminals.

Typically, design in prior art of cellular radio systems have been based on the requirements of mobile voice telephony service. However, the data transport requirements of an emerging new generation of broadband telecommunications. services to be offered on cellular radio system are much more demanding in terms of the cellular system channel quality. Examples of such new generation services are interactive multimedia such as video 20 conferencing, and video on demand. Two new data transport requirements that characterize the new generation services are guaranteed channel quality and DAMA channel assignment with short response times, typically measured in milliseconds or tens of milliseconds. Guaranteed channel quality means that 25 channels that are assigned to terminals are guaranteed to meet some specified channel quality criterion such as bit error rate.

The allocation of ever higher frequencies of the radio spectrum by the FCC enables the use of relatively narrower terminal antennas of reasonable cost and size. For example, spectral allocation for local multipoint distribution systems (LMDS) has been recently allocated at 28 Ghz, and for that application low-cost terminals with beamwidths of a few degrees is feasible. Narrow beams have known advantages in terms of mitigating multipath interference and reduction in the general level of cochannel interference.

It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

Summary of the Invention According to the invention there is provided a cellular radio communication system including a fixed master station communicating through wire, cable or other channels to each of a plurality of radio transmit-receive base stations; each base station having one or more sets of directional transmit receive antennas or antenna pairs, and each station connected through wire, cable or other channels to a long-range communications circuit; a plurality of radio transmit-receive terminal stations, each having a directive transmit-receive antenna unit oriented toward one nearby transmit station and containing o signaling circuits enabling it to request temporary assignment of use of a transmitreceive channel; eI -6each base station antenna unit connected to a multi-channel transmitter and receiver capable of simultaneously communicating, on separate transmit and receive channels, with a plurality of nearby terminal station whose antennas are directed toward the base station, and each such antenna is designed and oriented to communicate with terminal stations in a definite angular section which, when combined with a limitation on the maximum base station-terminal station distance, defines one communications "cell" of the system; said master station containing control elements designed to select and assign a frequency channel for each requested communication activity that will predicably control communications quality by limiting the amount of co-channel interference and of noise in the assigned channel.

The preferred embodiment of the present invention takes advantage of the fact that the proportion of significant co-channel interferers in the system is typically very small so that special treatment in channel assignment for that population is possible. The preferred embodiment of the present invention provides DAMA channel assignment i under a guaranteed channel quality criterion and with much higher spectral efficiencies than prior art. This is achieved in the preferred embodiment by measuring the cochannel interference characteristics of terminals.

Knowledge of terminal interference characteristics is used by the DAMA channel ooooo S• assignment algorithm of the preferred embodiment to control the co-channel interference in a systematic way so that all significant uplink co-channel interference is diverted into a relatively small number of unassigned channels. Similarly, the algorithm minimizes the number of downlink channel assignments that can induce significant down link -7co-channel interference, and prohibits the assignment of those channels. The preferred embodiment of the invention is applicable for example to LMDS systems.

A unique feature of the preferred embodiment of the invention is that its DAMA channel assignment procedure itilizes a database of prior information about the cochannel interference characteristics of terminals to assign channels in such a way that excessive co-channel interference gets harmlessly concentrated into a relatively small number of channels marked for interference and not assigned for communications. In this way the channel assignment algorithm is capable of offering guaranteed channel quality while avoiding the large frequency reuse numbers required in prior art to achieve such guarantees So* o g

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So *o* -8- In this way the preferred embodiment of the invention maintains a high level of spectral utilization efficiency.

The preferred embodiment of the invention provides for automated means to generate the database of prior information about terminal characteristics, and the database is also used to ensure that adjacent channel interference is not excessive and received signal power is adequate to meet the guaranteed channel quality criterion.

The preferred embodiment of the invention is based on two key observations about uplink co-channel interference when subscriber terminal antennas have narrow beamwidth: typically only a small proportion of terminals are significant co-channel interferers, and when a terminal is a significant co-channel interferer its transmissions typically only interfere with at most one nearby co-channel sector. In the preferred embodiment, the DAMA uplink •channel assignment procedure assigns channels to the relatively small number of subscribers known to be cochannel interferers in such a way that the co-channel 20 interference always falls in one of a relatively small number of channels reserved only for such interference.

o :The channels marked for interference are not assigned for eeoc communications in the sector in which the interference occurs so that significant co-channel interference is eoeeo 25 virtually eliminated from the channels assigned and used by terminals. Although the channels marked for interference represent wasted overhead, they are not only small in number relative to the totality of available channels, but -8aalso smaller in number than the population of terminals that are significant co-channel interferers. This is because under the DAMA assignment algorithm each unused channel marked for interference typically contains cochannel interference from more than one terminal. The preferred embodiment works similarly for downlink assignments except that the location of interferer and interfered radio is reversed; certain downlink channels are marked as unassignable in certain sectors because they cause co-channel interference in terminal receivers in neighbouring co-channel sectors.

Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed 15 in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to" S.Brief Description of Drawings A preferred embodiment of the invention will how be S 20 described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a diagram that illustrates the elements of e* the cellular radio system.

Fig. 2 is a diagram that illustrates the elements of a 25 base station.

Fig. 3 is a diagram that illustrates the elements of the 9 service center and net management.

Fig. 4 is a diagram that illustrates the elements of a subscriber terminal.

Fig. 5 is an example of a cellular plan.

Fig. 6 is an illustration of the geometry of uplink co-channel interference generated by interferers in sector 7c of Fig. Fig. 7 is an example table showing a calculation of spectral efficiency, for the invention versus conventional systems, for a given channel quality criterion and for R-squared propagation law.

Fig. 8 is an illustration of the tabular data contained in the channel assignment list.

Fig. 9 is a flow diagram of the DAMA channel assignment algorithm for the uplink.

Detailed Description of Preferred Embodiments Referring to Fig. I, the invention is a terrestrial cellular '20 radio system that comprises a plurality of base stations plurality of subscriber terminals [20] with narrow-beam antennas and a service center The base stations are o*l distributed over a service area in a spatial pattern that roughly approximates an idealized cellular plan. Each base station has a number M of sector antennas that radiate radially from the s* base station, where the number M is typically the same over 10 regions of the service area having the same subscriber density, and typical values of M are 3 (120 degree sectors), and 4 degree sectors), although omnidirectional antennas (M 1) are not excluded. Typically the sector antennas of a base station provide service coverage of a region centered at the base station. Each terminal communicates by line-of-sight or near line-of-sight radio wave propagation path [19] from terminal antenna [21] to an assigned base station sector antenna Trunk lines relay terminal communications data from base stations to the service center [30] where interconnection to telecommunications services occur.

Fig. 2 shows by way of typical example the structure of each base station. Each base station sector antenna is connected to a set of frequency division multiplexed (FDM) radio transmitters that generate a set of FDM radio channels for downlink digital communications. The FDM channel radio frequencies are a set F that is allocated to a sector. Similarly, each base station sector antenna is connected to a set of I. 20 FDM radio receivers having a set of FDM uplink radio S frequency channels for digital communications with allocated set G of radio frequencies.

One of the radio channels of an uplink FDM set is reserved for uplink net management (NM) data and all other radio channels of 25 the FDM set are assigned for uplink user data. Similarly, one of the radio channels of each downlink FDM set is reserved for *4IIII 11 downlink NM data and all other radio channels of the FDM set are assigned for downlink user data Each receiver of an FDM receiver set demodulates a digital data stream of an uplink channel where the data is uplink NM data [6a] for the NM channel, and uplink user data [6b] for all other channels of the FDM set. Additionally, the receiver for the uplink NM channel measures power in the NM channel, with resultant power measurement data Demodulated uplink data [6a] and [6b] are multiplexed [10] to form a downlink sector trunk [12] which is multiplexed [14] with all other downlink sector trunks of the base station to form the uplink base station trunk [16] which is routed to the service center. Similarly, but in the reverse direction, the downlink base station trunk [15] from the service center is demultiplexed [13] to yield downlink sector trunks [11] for each sector of the base station, and each downlink sector trunk [11] is further demultiplexed to yield the downlink NM data [7a] for the-downlink NM channel, and the user data [7b] for each of the downlink user data channels of the sector. The downlink data for each channel is modulated onto the channel waveform.by respective FDM channel transmitters Fig. 3 shows by way of typical example the structure of the .service center and the net management functions contained therein. At the service center [30] each incoming uplink base 25 station trunk [16] is demultiplexed [31] to obtain uplink data S for all uplink channels of all sectors of the base station, *9 SS 12 and power measurements for each NM channel of each sector of the base station. The uplink NM data [6a] and power measurements of each sector of each base station are routed by switch [33] to net management [40] in the service center, and the uplink user data [6b].is routed to service provider switches.

Switch control is exercised by the NM controller that has knowledge of the required switch mapping of trunk channels to terminals and the telecommunications services to terminals.

Similarly but in the reverse direction, downlink user data [7b] from service providers, and downlink net management data [7a] are switched [34] and multiplexed [32] into the appropriate base station trunk Generally for cellular radio systems, net management refers to control for efficient usage of cellular radio system resources, and the description of net management describes only novel net management functions or those functions that support novel or unique aspects of the invention. Net management is 'o coordinated by the controller and comprises two types of 5* 20 data processing elements: data bases which include the cellular frequency plan channel assignment list [43], terminal characteristics table and terminal sector assignments and algorithms for channel assignment [46], for power control, and for sector assignment The net 25 management elements are typically embodied in microprocessor firmware and executed by microprocessor and supporting data

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13 processing peripherals, but implementation in discrete.logic is also possible.

Fig. 4 shows by way of typical example the structure of a terminal. Each terminal [20] has a radio transmitter [22] with means to tune to any uplink FDM channel frequency of a sector and means to vary output power level. Each receiver [23] has means to tune to any downlink FDM channel frequency of a sector. Both transmitter and receiver are connected to the terminal antenna The terminal controller [24] controls uplink frequency, downlink frequency, and transmitter power level. The transmitter [22] modulates uplink digital data.[6] onto the uplink channel,.and if the channel is the NM channel, the digital data is uplink NM data [6a] that is routed by the switch from the terminal controller Otherwise, the uplink digital data is user data [6b] that is routed from an external data input/output port Similarly the receiver [23] demodulates

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downlink digital data from the downlink channel, and if the channel is the NM channel the digital data is downlink NM data 20 [7a] which is routed by switch [25] to the terminal controller; otherwise the data is downlink user data [7b] which is routed by switch [25] to the external user data input/output port Subscribers utilize the user data port [26] for interconnections of subscriber telecommunications user devices 25 such as phones, modems, personal computers, and multimedia devices with the telecommunications services interconnected at **ee: 0 @0 14 the service center.

Referring jointly to Figs. 3 and 4, the NM controller [41] controls terminals and their usage of system resources by two-way NM communications of NM messages [7a] with terminal controllers via base stations. Each terminal controller establishes a communications connection to the NM management controller when it tunes its transmitter [22] and receiver [23] to the net management channel of the sector assigned to the terminal. The sharing of a single net management channel by the multitude of terminals assigned to the sector may be managed by any suitable means known to those skilled in the art. For example, round-robin polling by the NM controller may be used for slow net management services such as terminal status monitoring, and random access used by terminals for rapid channel assignment requests. Uplink NM messages [6a] originating at a terminal that are relevant to the invention include service request, (2) 0e service logoff, and terminal status; messages, and net entry uplink. Downlink NM messages [7a] originating at the NM o° 20 controller that are relevent to the invention include service oe response, power control.

Referring to Fig. 3, the cellular frequency plan [31] in the service center net management is a database table that defines 25 the current allocation of FDM channel frequency groups to base station sectors. The uplink and downlink spectra allocated by the

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15 FCC to the cellular system are each partitioned into FDM channels. For the uplink, the channels are grouped into FDM channel groups Fl, FN, and similarly FDM channel groups Gl, G2, GN for the downlink. Each cell sector is allocated one of the downlink channel groups for the sector transmitter/set and one of the uplink channel groups for the sector receiver set and the aggregate allocations over the service area define the frequency reuse pattern or frequency plan.

An example of a cellular frequency plan suitable for narrowbeam antennas is shown in the example in Fig. 5. In Fig.

the cellular frequency reuse pattern is for square cells with M 4 90-degree sectors per cell, where base stations are labeled 1 through 9, and sectors are labeled a,b,c,d, so that sector c of base station 1 is labeled Ic, and so forth.

Polarization isolation is used to reduce co-channel interference, where V denotes vertical polarization, and H denotes horizontal polarization, but only one polarization is used per- sector so that P 1. There are N 2 frequency groups Fl and F2, and the assignment of frequency group Fi is denoted either Vi or Hi according to whether that frequency group is vertical or horizontal polarization. The.spectral utilization efficiency of the Fig. 5 example is E MP/N 200%.

Importantly, the invention is based on special properties of S* co-channel interference when narrow-beam terminal antennas are 16 used. By way of illustration of the special properties, Fig. 6 shows the conditions for a terminal in sector 7c to be an uplink co-channel interferer in one of three possible neighboring firsttier co-channel sectors. A terminal in sector 7c can be a cochannel interferer in a neighboring co-channel sector only if its narrow beam looks into the aperture of a co-channel sector with the same polarization, and this is possible only in sectors Ic, 3c or 9c in Fig. 5. Thus co-channel interference is possible only if the assigned sector and the co-channel sector line up in the narrow terminal beam. It is also evident in the geometry of Fig. 5 that for narrow-beam terminal antennas, a terminal can be a significant co-channel interferer in at most one co-channel sector. This implies that there is only a narrow strip of terminal locations around the perimeter of sector 7c where a 15 terminal can be a co-channel interferer. For randomly placed subscriber terminals in a sector, the proportion of terminals that are co-channel interferers will presently shown to be very small. The invention first determines which terminals are significant co-channel interferers by means of measurements in the following way.

The invention utilizes power control of transmitter power levels to achieve a system-wide uniform received signal power level S at base station sector receivers. The power control has two objectives minimize uplink adjacent channel interference in sector FDM receivers, and provide known power reference o 17 levels to enable accurate measurement of co-channel interference characteristics of terminals. Both objectives are important supporting features of the invention in providing guaranteed channel quality as presently described. The terminal controller [24] causes each terminal transmitter [22] to transmit status messages [6a] at roughly periodic intervals, either in response to polling messages [7a] from the NM controller [41) in the service center, or in synchrony with preassigned status message time slots in the uplink net management channel.. The power level of all status message are measured in the net management channel receiver of each base station sector. Based on power measurements received the power control algorithm [45] in the service center sends power directive NM messages to each terminal controller [24) to cause iterative adjustment of terminal transmitter power level until all signal power levels at all sector receivers converge to the same target power level S.

e After convergence of received terminal transmission to target power levels, the power control algorithm gathers measured power levels Ic [10] of each terminal's status message transmission in neighboring co-channel sectors, and the associated co-channel interference ratio S/Ic computed. If a terminal's status message transmissions cause measured co-channel S/Ic to fall below, or violates, a co-channel interference quality criterion Qc, the co-channel interference is termed significant, and the terminal termed an interferer; and the 18 corresponding sector in which the significant co-channel interference occurred is hereafter termed the jammed sector.

That is, there is associated with each interferer a jammed cochannel sector. The power measurement algorithm generates a table of terminal characteristics which tabulates by terminal ID following data: the assigned sector ID, whether a terminal is an interferer or a non-interferer, and if an interferer, the ID of the associated jammed sector wherein the terminal induces the significant level of co-channel interference.

The following is a description of the novel DAMA channel assignment algorithm of the invention for uplink channels; and the downlink channel assignment algorithm is analogous. At the instigation of a control signal [27] received by a terminal from its external user device, a terminal generates a service request :message [4a] which is received by the NM controller at the service center Referring to Fig. 3, the service request message implies a request for two resources jointly, (1) 20 interconnection to a specified telecommunications service at the service center, and channel assignment of base station FDM user channel resources as required to support the interconnection or data transport. The channel assignment is performed by the channel assignment algorithm [46] by searching for an available 25 channel in the channel assignment table [43] in the following way. The channel assignment table [43] is a state machine eo 19 representing current channel assignments and co-channel interference conditions in the system, and there are 2N subtables, one subtable for each uplink and downlink channel group and for each polarization used. Fig. 7 illustrates a subtable example for the Fig. 5 frequency plan, for frequency group Fl, with vertical polarization. The co-channel sectors in the subtable are 7c, Ic, 9c, and 3c. The row indices correspond to all the channels in the channel group Fl, and for simplicity only 8 channels are illustrated for the group as Cl, C2, C8.

The column heading give sector ID's for the four co-channel sectors. Each channel can be assigned at most once in each sector, so each sector has a column for marking channels that are assigned to terminals. Each channel in each sector can be jammed, suffer significant co-channel interference, so each sector has a second column to mark if a channel is jammed. The channel assignment algorithm marks a channel as assigned in a sector when the channel is assigned to a terminal in the sector.

If the terminal is an interferer, the channel must be marked as jammed in the column corresponding to the jammed sector. In this way the channel assignment subtable indicates the state of current assignments in all co-channel sectors and which channels are jammed in all co-channel sectors.

The channel assignment algorithm [46] utilizes the channel assignment table [43] to assign channels under a channel quality *oo constraint. Referring to Fig. 7, the following assignment 20 restrictions are evident. For a guaranteed channel quality criterion, the channel assignment algorithm may not assign a channel in a sector to any terminal if that channel is marked as jammed in that sector, or to an interferer terminal if that channel is currently assigned in the interferer's jammed sector. Restriction is necessary to avoid assignment in a channel containing significant co-channel interference that violates the channel quality criterion, and restriction is necessary to preclude the possibility that a new channel assignment may cause jamming of a currently assigned channel, thereby causing the currently assigned channel that previously met the quality criterion to now fail the quality criterion.

Relative to the Fig. 7 example, there are 2N-1 other subtables in the channel assignment table for the other 2N-1 channel groups, but all 2N-1 subtables are independent state machines because cochannel interference is confined to co-channel sectors Referring to Fig. 8, which illustrates a flow graph for the channel assignment algorithm for the uplink, the channel assignment algorithm first retrieves [50] the terminal characteristics, the terminal type (interferer or noninterferer), assigned sector ID, and if an interferer, the jammed sector ID. Then the channel assignment algorithm searches the terminal sector's channel assignment subtable, where the search procedure [51][52] starts at the bottom of the subtable if the terminal is an interferer, and starts at the top of the subtable o o•* 21 if the terminal is a non-interferer The channel assignment logic in either case obeys the restrictions described earlier associated with guaranteed channel quality criterion. The channel assignment algorithm optimally concentrates significant cochannel interference into the smallest number of jammed unassigned channels. Thus, for the case of interferer terminals, the search for channel assignments [51] initially attempts a channel assignment that causes the resultant co-channel interference generated by the terminal to fall on an already jammed channel in the jammed sector. The efficiency of concentrating co-channel interference into a few unassigned channels is further enhanced by maximal separation of interferers and non-interferers at opposite ends (top and bottom) of the channel assignment subtable by the channel assignment algorithm.

This is because when a jammed channel exists, concentration of a additional co-channel interference in the jammed channel implies additional assignment of channels in the same row of the subtable. If a non-interferer is assigned in the same row of the subtable, one potential opportunity for co-channel interference concentration is removed.

The channel quality criterion was based on a signal-to-cochannel interference metric. The invention applies to more general channel quality criteria. For example, for a channel quality criterion based on bit error rate (BER) metric, the a e channel quality criterion can be decomposed by techniques known 0C 22 to those skilled in the art into three joint criteria: (1) signal-to-co-channel interference ratio S/Ic Qc signalto-noise ratio S/N Qn, and signal-to-adjacent channel interference ratio S/Ia Qa. The channel assignment algorithm [46] ensures that each assigned channel meets criterion (1) relative to co-channel interference impairment. The criterion relative to thermal noise impairment can be implicitly met by setting the system wide target received power level S of the power control algorithm [45] high enough above the thermal noise level to meet the criterion. The criterion relative to adjacent channel interference impairment can be met by well-known waveform design techniques and channel spacing procedures known to those skilled in the art. In this waythe invention provides for a guaranteed BER quality criterion The efficiency of the channel assignment algorithm is computed as follows for narrow-beam terminal antennas. For a given channel quality criterion, the proportion W of terminals that are interferers is first determined. Because the algorithm 20 concentrates co-channel interference into the unassigned jammed channels, and each interferer terminal jams at most one cochannel sector, the overhead associated with unassigned, jammed channels is upper-bounded by W. Hence for efficiency E associated with a cellular frequency plan, the net spectral 25 efficiency of the invention greater than E(1-W) But for narrow-beam antennas, W is small (much less than one) so that o 23 E(1-W) Thus, the idea of the invention is to start with a frequency plan with associated high spectral efficiency E that causes co-channel interference levels to be present in the system at a level that violate the channel quality criterion. However, the channel assignment algorithm will ensure through measurements that the channels with significant co-channel interference levels will not be assigned to terminals.

In order to demonstrate the benefits of the invention numerically, the table of Fig. 9 shows a simplified comparison of efficiency and achievable channel quality criteria for both conventional DAMA channel assignment algorithm and the invention algorithm for.the special case where propagation loss is proportional to range-squared. Two frequency plans are considered, the plan in Fig. 5 with efficiency E 200%, and a modification of Fig. 5 in which all frequencies are assigned to each sector (N 1) so that E 400%. The second column of the table indicates the distance ratio r which is the minimum O* distance ratio of base station-to-co-channel interferer over 20 base-station-to-assigned terminal. The conventional algorithm is assumed to be one that simply assigns any channel that is unassinged in the terminal's assigned sector. The conventional algorithm can guarantee any channel quality criterion Qc for signal-to-co-channel interference ratio only if Qc s_201og(r) at spectral efficiency E, and this is indicated.in column 3. For Qc 2 0log(r) the conventional algorithm cannot meet the channel 24 quality criterion at any spectral efficiency level. The invention can do as well as the conventional algorithm for Qc s and can meet larger fidelity criteria as well at a small cost in overhead w. For example, for a quality criterion of Qc 14 dB, the invention can use the frequency plan with frequency reuse number N 1 and efficiency E 400%. This is at a calculated overhead of W .04 for an assumed beamwidth.of 3 degrees. Thus, the net efficiency for the invention is E(l-W) 384% for Qc 14 dB. The conventional system-is required to use the frequency reuse number N 2 for quality criterion Qc 14 dB, with resultant spectral efficiency E 200%.

The preceding description of the novel DAMA channel assignment algorithm applied to the uplink. For the downlink, the channel algorithm is analogous where the role of the interferer and the object of interference is reversed relative to the case for the uplink. Thus for downlink assignments, each terminal is labeled as either susceptible to co-channel Sinterference or non-susceptible, and for each susceptible 20 terminal there is the associated sector which is the source of the interference, and which is recorded in the terminal characteristics database. The downlink channel assignment table is analogous to the uplink channel assignment table of Fig. 7, with each column for marking of forbidden jammed channels on the ee uplink replaced with a column for marking of forbidden jamming channels on the downlink. The downlink channel assignment 25 algorithm is analogous to the uplink channel assignment algorithm of Fig. 8 in an obvious way. For example, if a terminal is susceptible to co-channel interference, the algorithm first looks at the assignments in the interfering sector and attempts to find a forbidden channel that is marked as an interferer, for assignment in the terminal's sector. The spectral efficiency of the algorithm for the downlink is computed analogously and hence is as efficient as the uplink if the same modulation, quality criterion, and frequency plan is used.

The invention is extendable in ways obvious to those skilled in the art to the case where terminal narrowbeam antennas are steerable as in phased arrays and terminal motion occurs only between channel assignments.

The invention is extendable in ways obvious to those skilled S. in the art to the case where each of the FDM channels may be partitioned into smaller spectral units for assignment such as time-division slots, or code-division channels.

While preferred embodiments of the invention have been 20 described and illustrated, other embodiments, modifications and adaptations of the invention will be readily apparent to those skilled in the art.

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Claims (2)

1. A cellular radio communication system including a fixed master station communicating through wire, cable or other channels to each of a plurality of radio transmit-receive base stations; each base station having one or more sets of directional transmit receive antennas or antenna pairs, and each station connected through wire, cable or other channels to a long-range communications circuit; a plurality of radio transmit-receive terminal stations, each having a directive transmit-receive antenna unit oriented toward one nearby transmit station and containing signaling circuits enabling it to request temporary assignment of use of a transmit- receive channel; each base station antenna unit connected to a multi-channel transmitter and receiver capable of simultaneously communicating, on separate transmit and receive S° 15 channels, with a plurality of nearby terminal stations whose antennas are directed toward the base station, oeee• and each such antenna is designed and oriented to communicate with terminal stations in a definite angular section which, when combined with a limitation on the .maximum base station-terminal station distance, defines one communications "cell" of 20 the system; said master station containing control elements designed to select and assign a frequency channel for each requested communication activity that will predicably control communications quality by limiting the amount of co-channel interference and of noise in the assigned channel. -27-

2. A cellular radio communications system substantially as herein described with reference to any one of the disclosed embodiments and their associated drawings. DATEDthis 21st Day of February, 2001 STANFORD TELECOMMUNICATIONS, INC. Attorney: PHILLIP DAVID PLUCK Registered Patent Attorney of The Institute of Patent and Trade Mark Attorneys of Australia of BALDWIN SHELSTON WATERS *e e e