GB2306083A

GB2306083A - TDMA communication system

Info

Publication number: GB2306083A
Application number: GB9620744A
Authority: GB
Inventors: Katsuhiko Kawazoe; Masato Mizoguchi; Shuji Kubota; Takeshi Hattori
Original assignee: Nippon Telegraph and Telephone Corp
Current assignee: Nippon Telegraph and Telephone Corp
Priority date: 1995-10-06
Filing date: 1996-10-04
Publication date: 1997-04-23
Anticipated expiration: 2016-10-04
Also published as: GB9620744D0; GB2306083B; CN1080956C; CN1157508A; HK1008765A1

Abstract

In a TDMA communication system, a number of time slots used for communication is increased with no increase of transmitters and receivers, and further high rate transmission is also provided. Transmission and reception are carried out simultaneously in each time slot with different frequencies. The bandwidths for transmission and reception are independently variable by multiple time slot allocation, and the carrier frequency for each time slot for transmission and the carrier frequency for each time slot for reception are assigned for each time slot for communication. The carrier frequency for a time slot for reception is used also for the carrier frequency for a time slot for transmission spaced therefrom by a predetermined time spacing.

Description

TDMA COiMUNICATION SYSTEM The present invention relates to a TDMA (Time Division Multipul Access) communication system.

In PHS (Personal Handy Phone System; RCR STD-28) system, TDMA-TDD system is used, in which communication is carried out on time division duplex, and the same carrier frequency is used both for up-link and down-link. In TDMA-TDD system in PHS system, the TDMA frame is 5 msec, which is divided to 8 time slots so that 4 time slots are assigned to down-link (from a base station to terminals), and 4 time slots are assigned to up-link (from terminals to a base station). The transmission bit rate is 384 kbps.

Fig.l shows a time slot allocation of TDMA-TDD system in PHS system. In TDMA-TDD system, the transmission carrier frequency in a base station is the same as that in a terminal station, and thereby, transmission diversity system is useful for overcoming degradation of reception signal quality in a terminal station due to multipath fading channel ("Floor Error Reduction by Transmitter diversity in TDMA/TDD Systems", B-304, 1992 Spring Conference in Institute of Electronics, Information and Communication Engineers in Japan). In transmission diversity system, transmission carrier frequency must be the same as reception carrier frequency, antenna selection is carried out in a base station but a terminal station does not need to have a plurality of antennas, and therefore, it is useful to miniaturize a terminal station and save its power consumption.

In TDMA-TDD system in PHS system, four time slots are used for transmission and reception, respectively, between a base station and terminal stations as shown in Fig.l.

Fig.l shows an example that terminal stations (a), (b), (c) and (d) are communicating with a base station simultaneously. In the figure, the time slots 1, 2, 3 and 4 are used for communication from terminals (a), (b), (c) and (d), respectively, to a base station. The time slots 5, 6, 7 and 8 are used for communication from a base station to the terminals (a), (b), (c) and (d), respectively. In PHS system, transmission carrier frequency and reception carrier frequency used between a base station and a terminal are the same as each other, and time spacing of a transmission time slot from a base station to a terminal and a transmission time slot from the terminal to the base station is separated by four time slots (2.5 msec).In a practical PHS system, one pair time slot out of four pair time slots is used for transmission of control channel used commonly between a base station and terminals, and three pair of time slots are available for communication between a base station and terminals, however, it is assumed in the present specification that all the four pair time slots are used between a base station and terminals to distinguish clearly the present invention from a prior art.

When traffic is dense, it is desired that a base station can communicate with more terminal stations. In that case, two transmitters and two receivers are used so that two frequencies are assigned.

Fig.2 shows a system (prior art) in which eight time slots are used between a base station and terminals, and the terminals (a), (b), (c), (d), (e), (f), (g), and (h) are communicating with a base station simultaneously.

The communication between a base station and terminals (a), (b), (c) and (d) uses the carrier frequency fl, and the communication between a base station and terminals (e), (f), (g) and (h) uses the carrier frequency f2.

Fig.3 shows the structure of a base station in the prior art of Fig.2. The base station has a pair of transmitters and a pair of receivers (T1, T2, R1, R2) which are switched by a switch for simultaneous transmission and simultaneous reception by using different carrier frequencies. The symbol A shows an antenna.

On the other hand, when TDMA system is used, TDMA-FDD system (Time Division Multiple Access - Frequency Division Duplex ) has been known. That system has more time slots in a TDMA frame than TDMA-TDD system. That system communicates with time division basis, and transmission carrier frequency differs from reception carrier frequency. The personal digital cellular (PDC; RCR STD-27A) uses the TDMA-FDD system.

Fig.4 shows an example of TDMA-FDD system, in which a TDMA frame is 5 msec which is the same as that of PHS system, and the frame is divided to 8 time slots so that 8 time slots are assigned to down link and 8 time slots are assigned to up link. The transmission carrier frequency of a base station differs from the transmission carrier frequency of a terminal station. In the example of Fig.4, the transmission carrier frequency of a base station is fl, and the transmission carrier frequency of a terminal station is f2.

Fig.5 shows structure of a tranceiver for TDMA-FDD system. The symbol A is an antenna, D is an antenna duplexer, T is a transmitter, and R is a receiver. A duplexer as shown in the figure is necessary in TDMA-FDD system, since transmission is carried out at the same time as reception.

However, the prior TDMA-FDD system in which the duplexer has fixed transmission frequency band and fixed reception frequency band canrl be used irlt}se PHS system in which transmission carrier frequency is the same as reception carrier frequency.

As mentioned above, in a conventional PHS system, when a number of terminals that each base station communicate simultaneously is to be increased, a plurality of transmitters and a plurality of receivers are essential, and therefore, hardware in the base station must be complicated.

By the way, in a personal portable communication system in which cordless telephone system like PHS system has developed, the use for multimedia communication is desired because of high transmission rate. For instance, the PHS system has the specification of bearer data transmission of 32 kbps, and 64 kbps communication is being introduced by using two time slots. However, when the higher rate communication is requested, it is only possible to provide 128 kbps (=32x4) by using one carrier frequency of four time slots, as far as the current frame format is kept. However, that rate can not satisfy the transmission capacity of ISDN basic unit (2B+D = 144 kbps), and therefore, the use of PHS system to multimedia communication using personal portable communication system is considerably restricted.

Therefore, it has been desired to provide the transmission capacity for basic ISDN service link by using a frame format of conventional PHS.

In accordance with one aspect of the present invention, a method for TDMA communication comprises carrying out transmission and reception simultaneously using different carrier frequencies, wherein the frequency band of a time slot for reception and the frequency band of the time slot for transmission are variable, the carrier frequency of a time slot for reception and the carrier frequency of the time slot for transmission are variable, and the carrier frequency used in a time slot for reception is used for transmission in a time slot with a predetermined time spacing.

In accordance with a second aspect of the present invention, a TDMA communication equipment for TDMA communication system comprises: 1) means for simultaneous transmission and reception in each time slot, 2) means for varying the frequency band for transmission and the frequency band for reception, and 3) means for varying the carrier frequency in a reception time slot and the carrier frequency in a transmission time slot, wherein the carrier frequency used in a time slot for reception is used for transmission in a time slot with a predetermined time spacing.

The present invention enables the number of terminals connected simultaneously to a base station to be increased.

The present invention also provides high rate communication in data communication to provide basis ISDN service link (144 kbps).

The present invention is compatible with a conventional TDMA-TDD system (for instance PHS system). In a conventional PHS system, time slots for reception are separated from time slots for transmission in every 4 time slots, and no simultaneous operation for transmission and reception is carried out. However, in order to increase the number of terminals for each base station, and to provide high rate communication, simultaneous operation of transmission and reception is essential, and the number of time slots must be increased. The present invention achieves this. Further, since the carrier frequency used in a time slot for reception is used for transmission in a time slot with a predetermined time spacing, the system is compatible with the conventional PHS system.

Some examples of methods and apparatus according to the invention will now be described with reference to the accompanying drawings, wherein: Fig.l shows time slot allocation of a prior TDMA-TDD system in PHS system, Fig.2 shows time slot allocation of a prior TDMA-TDD system where there are eight time slots, Fig.3 shows structure of a base station in a prior TDMA-TDD system, Fig.4 shows time slot allocation of a prior TDMA-FDD system when there are eight time slots, Fig.5 shows a base station in a prior TDMA-FDD system, Fig.6 shows an example of a time slot assignment embodying the present invention when there are eight time slots, Fig.7A shows structure of a TDMA communication apparatus according to the present invention, Fig.7B shows another structure of a TDMA communication equipment according to the present invention, Fig.8 shows an embodiment of characteristics of an antenna duplexer, Fig.9 shows a waveform of switching signal, Fig.10 shows a modification of a duplexer part according to the present invention, Fig.ll shows another modification of a duplexer portion according to the present invention, Fig.12 shows still another modification of a duplexer portion according to the present invention, Fig.13 shows an example of assignment of time slots when high rate channel (192 kbps) is established according to the present invention, Fig.14 shows an assignment of time slots when a channel in Fig.13 is used for basic ISDN service link, and Fig.15 shows an assignment of time slots when transmission rate in an up link differs from that in a down link.

(Embodiment 1) Now, an embodiment of a base station in PHS system having a single transmitter and a single receiver, capable to communicate simultaneously with 8 terminal stations, is described.

Fig.6 shows an assignment of time slots and carrier frequencies for communication between a base station and terminal stations. The number of time slots for communication between a base station and terminal stations is eight, and the terminal stations (a), (b), (c), (d), (e), (f), (g), and (h) are communicating with a base station simultaneously. In PHS system, transmission carrier frequency of a base station to a terminal station is the same as reception carrier frequency from said terminal station, as described in background of this specification.

Alough the prior art of liy. 2 uses i:wo different carrier frequencies for a down link from a base station to a terminal and an up link from a terminal to a base station, the number of carrier frequencies used simultaneously for transmission and reception is one at a time.

In Fig.6, in a first time slot 1, the transmission carrier frequency from a terminal to a base station is f7, and the transmission carrier frequency from a bdse station tu a terminal is fj.

In a terminal station side, a time slot for transmission is spaced by 4 time slots (2.5 msec) from a time slot for reception as is the case of a prior art, and as a terminal station does not need to transmit and receive simultaneously, a terminal station may be small in size and consumes less power.

While in the prior art in Fig.2, when a base station handles 8 terminals, the number of transmitters and receivers must be increased, in the present invention, no increase of a transmitter and a receiver is necessary, and a base station may be small in size and consumes less power.

Fig.7A shows a block diagram of a TDMA communication equipment according to one embodiment The TDMA communication equipment according to the present invention has a pair of duplexers D1, D2, and a switching control signal (CONT) selects each duplexer. Therefore, it should be appreciated that carrier frequency for transmission and carrier frequency for reception are not fixed, while those frequencies in the prior art in jig.4 dre fixed. In the embodiment, it is assumed that the duplexers have transmission frequency band and reception frequency band as shown in Fig.8, and the duplexers are switched for each time slot for communication.The duplexer D1 has transmission carrier frequency fl-f5, and reception carrier frequency f6-f10. The duplexer D2 has reception carrier frequency fl-f5, and transmission carrier frequency f6-f10. The switching control signal is shown in Fig.9 for providing assignment of time slots in Fig.6. In the time slots 1-4, the duplexer D1 is used, and in the time slots 5-8 the duplexer D2 is used.

In the embodiment of Fig.6, a transmitter T provides signals for eight channels in eight time slots with the frequencies f3, fl, fl, fl, f7, f7, f7 and f9. The second switch SW2 connects an output of the transmitter T to the first duplexer D1 at the first four time slots, and to the second aup'exer D2 at the other foul time slots 5-8. The first switch SW1 selects the first duplexer D1 at the time slots 1-4, and therefore, the carrier frequencies f3 and fl are radiated from the antenna A, and the first switch SW1 selects the second duplexer D2 at the time slots 5-8, and therefore, carrier frequencies f7 and f9 are radiated.

The operation for reception is similar. The first duplexer D1 is selected at the time slots 1-4 so that the carrier frequencies f7 and f9 are applied to the input of the receiver R through the third switch SW3, and the second duplexer D2 is selected at the time slots 5-8 so that the carrier frequencies f3 and fl are applied to the input of the receiver R through the third switch SW3.

In Fig.7A, the portion enclosed by a dotted line including a pair of duplexers D1 and D2, switches SW1, SW2 and SW3 is called a duplexer part DP. The duplexer part DP receives transmission signal t from a transmitter T, and supplies receive signal r to a receiver R. It receives a control signal C for each switches.

Fig.7B shows a block diagram of a base station when a transmission diversity method for TDMA communication system is used in a base station. In Fig.7B, a pair of dulee parts DP1 and DP2 are provided.

The receive signals r in each duplexer part are applied to the receivers R1 and R2, respectively, where received signal quality is measured, and according to the measured signal quality, the switch control (SW CONT) switches the selector (SEL) and the transmission switch (SW) so that the receiver (R1 or R2) with the better receive signal quality is selected in a reception side, and the same duplexer part (DP1 or DP2) used in a reception side for a carrier frequency in each time slot is selected in a transmission side. The measure of receive signal quality is conventional, and may be carried out by measuring receive level, or error rate, et al.

The TDMA control (TDMA CONT) in rig. 7B is conventional. It functions to supply a TDMA signal in each time slot to a transmitter T, to receive a signal from a receiver R, and to generate switching control signal (CONT) which synchronizes with a time slot.

Fig.10 shows a modification of a duplexer part DP which has only one duplexer D, and has the same operation as that of Fig.7A. The switch matrix (SW1, SW2, SW3 and SW4) switches the first case where transmission signal generated in the transmitter T is applied to the terminal A of the duplexer D which passes carrier frequencies fl-f5 in the duplexer D and receive signal of the carrier frequencies f6-f10 at the terminal B is applied to the receiver R, and the second case where the transmission signal is applied to the terminal B of the duplexer D and the signal appearing at the terminal A of the duplexer D is applied to the receiver R. In Fig.9, during time slots 1-4, each switch connects the first contact 1, so that carrier frequencies fl-f5 are transmission frequency band and carrier frequencies f6-f10 are receive frequency band.

And, during time slots 5-8, each switch connects the second contact 2, so that carrier frequencies fl-f5 are receive frequency band, and carrier frequencies f6-f10 are transmission frequency band. As output terminals (A, B) of the duplexer D are used both for transmission and reception, the frequency tuning characteristics must be satisfied both for transmission and reception. A conventional duplexer has a fixed transmission bandwidth that a terminal has small insertion loss, and a fixed reception bandwidth that a terminal has large attenuation out of the band.

Fig.ll shows a modification of a duplexer part DP, which is used when an isolation between transmission side and reception side in Fig.10 or Fig.7A is insufficient, because of leakage power in OFF state of a switch. In the structure of Fig.7A, when the duplexer D1 is selected, the transmission carrier frequency is one of frequencies fl-f5, and the transmission carrier frequency is radiated through the contact (1) of the switch SW1, and the antenna. However, the transmission signal leaks to the contact (2) of the switch SW1. The level of the leakage power is generally -20 dB in an ordinary switch in microwave band in a mobile communication system.The transmission power leaked to the contact 2 from the contact 1 of the switch SW1 is applied to the contact 2 of the third switch SW3 through the pass band terminal of the duplexer D2. Although the contact 2 of the third switch SW3 is in OFF state, it leaks a signal to the receiver R with the attenuation -20 dB. As a result, transmission signal is applied to a receiver with attenuation of -40 dB because of leakage in OFF state of the switches SW1 and SW3. When the undesired leakage level due to the transmission signal does not satisfy the desired characteristics in a receive side, the isolation between transmission side and reception side is improved by using the structure of Fig.ll.

Fig.ll is modified from Fig.7A that a bandpass filter and a power amplifier at an output of a transmitter T in Fig.7A (not shown in Fig.7A) are relocated between duplexers D1 and D2, and a second switch SW2, and a front end amplifier and a bandpass filter at an input of a receiver in Fig.7A (not shown in Fig.7A) are relocated between duplexers D1 and D2, and a third switch SW3. When the structure of Fig.ll is taken, and a power amplifier and a front end amplifier are switched ON or switched OFF at the same time as the control of each switches, undesired leakage pass is cutoff as a related amplifier is switched OFF. An amplifier has a predetermined gain when a power supply is supplied, and the gain is zero when the power supply is not supplied.For instance, in the structure of Fig.7A, when the duplexer D1 is selected, transmission signal leaked to the contact 2 of the first switch SW1 is applied to the contact 2 of the third switch SW3 through the passband terminal of the duplexer D2, on the other hand, in the structure of Fig.ll, as the front end amplifier RX2 is switched OFF, the undesired leakage signal applied to the front end amplifier is attenuated by the ON/OFF ratio of the front end amplifier.

Fig.12 is the modification of Fig.ll, in which a first switch SW1 is replaced by a circulator C. A circulator C has three terminals 1-3 so that an input signal to a terminal 1 is output to a terminal 2, an input signal to a terminal 2 is output to a terminal 3, and an input signal to a terminal 3 is output to a terminal 1.An output of a power amplifier TX1 (which is applied to a terminal A of a duplexer D1 in Fig.ll) is connected to a bandpass filter having the frequency band fA of the passband fl-f5 , and an output of a power amplifier TX2 (which is applied to a terminal B of a duplexer D2 in Fig.ll) is connected to a bandpass filter having the frequency band fB with the passband f6-f10, and the outputs of both the bandpass filters are connected to the terminal 1 of the circulator C. The terminal 2 of the circulator C is connected to an antenna. With that structure, an output of a transmitter is amplified by a power amplifier TX1 or TX2 depending upon the switching control signal, passes a bandpass filter fA or fB, and is applied to a circulator C through the terminal 1 of the same. An output of the circulator C is radiated in air through an antenna A. On the other hand, in reception side in Fig.12, a signal received by an antenna A is output from a terminal 3 of a circulator C, and the terminal 3 of the circulator C is connected to a front end amplifier RX1 through a bandpass filter fA which passes fl-f5 and a front end amplifier RX2 through a bandpass filter fB which passes f6-fl0, instead of a duplexer 2 of Fig.ll.

Therefore, a signal received by an antenna selects one of the frequency bands fA and fB so that the selected frequency band is not transmission band, and the selected frequency band is applied to a receiver through a front end amplifier.

Fig.13 shows an example of assignment of time slots when high rate channel is used. As each time slot provides 32 kbps, 192 kbps is obtained by using 6 time slots in the embodiment of the figure. The time slots 2, 4, 5, 6, 7 and 8 are used for transmission from a terminal to a base station, and the time slots 1, 2, 3, 4, 6 and 8 are used for transmission from a base station to a terminal.

In an up link from a terminal to a base station, a time slot uses four kinds of carrier frequencies (f7, f9, f3 fl, fl, fl), and in a down link from a base station to a terminal, a time slot also uses four kinds of carrier frequencies (f3, fl, fl, fl, f7, f9). Therefore, all the carrier frequencies used in transmission in a base station are included in the transmission carrier frequencies by a terminal. This makes possible to take transmission diversity system in a base station.

On the other hand, when only three carrier frequencies which are part of four carrier frequencies used in an up link, are used for transmission in a down link (transmission in the sequence of f3, fl, fl, fl, f7, f7), a transmission diversity system is also possible.

Thus, a down link from a base station to a terminal may use, with a predetermined time spacing, all or a part of the carrier frequencies used in an up link from a terminal to a base station.

A time slot which is not used for high rate channel may be used for a conventional PHS terminal, and the time spacing between a transmission time slot and a reception time slot is 4 time slots (slots 1 and 5, and slots 3 and 7).

Fig.14 shows an example of assignment of time slots when a circuit in Fig.l3 is used as a basic ISDN service link. In the figure, two time slots correspond to Bl-channel, other two time slots correspond to B2-channel, and another time slot corresponds to D-channel.

A carrier frequency used for transmission in a base station is used further for reception in the base station, and therefore, transmission diversity system is possible.

Fig.15 shows an example of assignment of time slots when transmission rate in up link differs from that in down link. In the embodiment, two time slots are assigned in transmission from a terminal to a base station, and six time slots are assigned in transmission from a base station to a terminal. Other time slots are used for conventional PHS system, and time spacing between a transmission time slot and a reception time slot is 4 time slots (time slots 4 and 8).

In case of a data communication between a terminal and an information server, low rate channel is enough for an up link for transmission of a command to the information server, however, high rate channel is necessary for down link for transmission of large data derived from the information server. Fig.15 shows an example of assignment of time slots for asymmetrical transmission in which transmission capacity in up link differs from that in down link.

(Embodiment 2) The Broadband PCS band Plan (IEEE Personal Communications pp.36-43, fourth quarter, 1994 vol.l No.4) in U.S.A. determines frequency bands 1850-1910 MHz, and 1930-1990 MHz for PCS (Personal Communication Services) which needs a license.

The present invention is used in that plan by assigning at least a part of 1850-1910 MHz to transmission frequency band of a duplexer D1 and reception frequency band of a duplexer D2 in the embodiment 1, and at least a part of 1930-1990 MHz to reception frequency band of a duplexer D1 and transmission frequency band of a duplexer D2 in the embodiment 1.

(Embodiment 3) The frequency band 1850-1910 MHz in the embodiment 2 overlaps with 1895-1918 MHz in PHS system used in Japan.

Therefore, it would be possible to start conventional PHS system in 1895-1910 MHz, and then, to use the system of the present invention by using 1985-1910 MHz and other frequency bands in Broadband PCS Band. That method makes it possible to use conventional PHS system in countries other than Japan, and further to use frequency bands which are not used in conventional PHS system.

As described above in detail, according to the present TDMA communication system, each time slot is used both for transmission and reception, and carrier frequency used in transmission is also used in reception. Thus, the number of time slots in radio communication in TDMA system is increased with no increase of transmlitezs and receivers. Therefore, the number of terminal s-.a; olls for each base station is increased, and further, high rate data communication which satisfies basic ISDN service link (144 kbps) is implemented.

From the foregoing, it will now be apparent that a new and improved TDMA communication system has been found.

Claims

1. A method for TDMA communication comprising carrying out transmission and reception simultaneously using different carrier frequencies, wherein the frequency band of a time slot for reception and the frequency band of the time slot for transmission are variable, the carrier frequency of a time slot for reception and the carrier frequency of the time slot for transmission are variable, and the carrier frequency used in a time slot for reception is used for transmission in a time slot with a predetermined time spacing.

2. A method for TDMA communication according to claim 1, wherein communication is carried out between a base station and a terminal station, said base station transmitting a signal in down link to said terminal station with a predetermined time spacing after receiving a signal in up link from said terminal station, at least a part of the carrier frequencies used in said link being used for the carrier frequency in said down link, and wherein said base station operates with the steps of: 1) receiving a signal in said up link with a plurality of antennas, 2) measuring received signal quality through each of said antennas, 3) selecting the antenna which provides the highest result of said measurement, and 4) transmitting a signal in down link with said selected antenna.

3. A TDMA communication equipment for TDMA communication system, the equipment comprising: 1) means for simultaneous transmission and reception in each time slot, 2) means for varying the frequency band for transmission and the frequency band for reception, and 3) means for varying the carrier frequency in a reception time slot and the carrier frequency in a transmission time slot, wherein the carrier frequency used in a time slot for reception is used for transmission in a time slot with a predetermined time spacing.

4. A TDMA communication equipment according to claim 3, the equipment comprising a base station having: means for receiving a signal in up link from a terminal station which has said TDMA communication equipment with a plurality of antennas, means for measuring received signal quality, means for selecting the antenna which provides the highest result of said measurement, and means for transmitting a signal in down link with the selected antenna with a predetermined time spacing from reception of said signal in said up link.

5. A TDMA communication equipment for TDMA communication system according to claim 3 or claim 4, wherein said equipment has a first and a second duplexer, a first switch for selecting one of the duplexers to connect to an antenna, a second switch for connecting an output of a transmitter to one of said duplexers, a third switch for connecting an input of a receiver to one of said duplexers, and a terminal for accepting a control signal for controlling said switches.

6. A TDMA communication equipment for TDMA communication system according to claim 3 or claim 4, wherein: said equipment has a duplexer which is connected to an antenna and has a first terminal A having one of the frequency bands and a second terminal B having the other frequency band, and a switching matrix provided between said duplexer, and a transmitter and a receiver, said switching matrix having a first switch for switching a signal input or output to or from said first terminal A, a third switch for switching a signal input or output to or from said second terminal B, a second switch for connecting an output of a transmitter to one of said first switch and said third switch, a fourth switch for connecting an output of a receiver to one of said first switch and said third switch, and a terminal for accepting a control signal for controlling said switches.

7. A TDMA communication equipment for TDMA communication system according to claim 3 or claim 4, wherein said equipment comprises: a first and a second duplexer, a first switch for connecting one of said duplexers to an antenna, a second switch for connecting an output of a transmitter to a first contact or a second contact, a third switch for connecting an input of a receiver to one of two inputs, a first bandpass filter having a first pass band (fA) connected to a first contact of said second switch, a first power amplifier for connecting an output of said first bandpass filter to a first terminal of said first duplexer, a second bandpass filter having a second pass band (fB) connected to a second contact of said second switch, a second power amplifier for connecting an output of said second bandpass filter to a second terminal (B) of said second antenna duplexer, a first front end amplifier for amplifying a signal at a second terminal (B) of said first duplexer, a third bandpass filter having a second pass band (fB) connected to an output of said first front end amplifier, a second front end amplifier for amplifying a signal at a first terminal (A) of said second duplexer, a fourth bandpass filter having a first pass band (fA) connected to an output of said second front end amplifier, means for connecting outputs of said third bandpass filter and said fourth bandpass filter to a first contact (1) and a second contact (2), respectively, of said third switch, a terminal for receiving a control signal for controlling said switches, said power amplifiers and said front end amplifiers, wherein said first and second power amplifiers are controlled so that gain of one of said power amplifiers is zero when the other power amplifier has certain gain, and gain of one of said front end amplifiers is zero when the other front end amplifier has certain gain.

8. A TDMA communication equipment for TDMA communication system according to claim 7, wherein operation of said first switch is carried out by a circulator, and operation of said first and second duplexers is carried out by combination of the first and second bandpass filters.

9. A method for TDMA communication substantially as hereinbefore described with reference to any of the examples described in Figures 6 to 15 of the accompanying drawings.

10. A TDMA communication equipment for TDMA communication system substantially as hereinbefore described with reference to any of the examples described in Figures 6 to 15 of the accompanying drawings.

Amendments to the claims have been filed as follows 1. A method for TDMA communication comprising carrying out within a time slot simultaneous transmission and reception using different carrier frequencies, wherein the reception frequency band of a time slot and the transmission frequency band of a time slot may be varied between time slots, the reception carrier frequency of a time slot and the transmission carrier frequency of a time slot may be varied between time slots, and the carrier frequency used in at least one time slot for reception is used for transmission in a time slot spaced therefrom by a predetermined time spacing.

2. A method according to claim 1, wherein the simultaneous transmission and reception are carried out at a base station.

3. A method for TDMA communication according to claim 1 or claim 2, wherein communication is carried out between a base station and a terminal station, said base station transmitting a signal in down link to said terminal station with a predetermined time spacing after receiving a signal in up link from said terminal station, at least a part of the carrier frequencies used in said link being used for the carrier frequency in said down link, and wherein said base station operates with the steps of: 1) receiving a signal in said up link with a plurality of antennas, 2) measuring received signal quality through each of said antennas, 3) selecting the antenna which provides the highest result of said measurement, and 4) transmitting a signal in down link with said selected antenna.

4. A TDMA communication equipment for TDMA communication system, the equipment comprising: 1) means for simultaneous transmission and reception in each time slot, 2) means for varying the reception frequency band and the transmission frequency band between time slots, and 3) means for varying the reception carrier frequency of a time slot and the transmission carrier frequency of a time slot between time slots, wherein the carrier frequency used in at least one time slot for reception is used for transmission in a time slot spaced therefrom by a predetermined time spacing.

5. Apparatus according to claim 4, wherein the simultaneous transmission and reception are carried out at a base station.

6. A TDMA communication equipment according to claim 4 or claim 5, the equipment comprising a base station having: means for receiving a signal in up link from a terminal station which has said TDMA communication equipment with a plurality of antennas, means for measuring received signal quality, means for selecting the antenna which provides the highest result of said measurement, and means for transmitting a signal in down link with the selected antenna with a predetermined time spacing from reception of said signal in said up link.

7. A TDMA communication equipment for TDMA communication system according to any of claims 4 to 6, wherein said equipment has a first and a second duplexer, a first switch for selecting one of the duplexers to connect to an antenna, a second switch for connecting an output of a transmitter to one of said duplexers, a third switch for connecting an input of a receiver to one of said duplexers, and a terminal for accepting a control signal for controlling said switches.

8. A TDMA communication equipment for TDMA communication system according to any of claims 4 to 6, wherein: said equipment has a duplexer which is connected to an antenna and has a first terminal A having one of the frequency bands and a second terminal B having the other frequency band, and a switching matrix provided between said duplexer, and a transmitter and a receiver, said switching matrix having a first switch for switching a signal input or output to or from said first terminal A, a third switch for switching a signal input or output to or from said second terminal B, a second switch for connecting an output of a transmitter to one of said first switch and said third switch, a fourth switch for connecting an output of a receiver to one of said first switch and said third switch, and a terminal for accepting a control signal for controlling said switches.

9. A TDMA communication equipment for TDMA communication system according to any of claims 4 to 6, wherein said equipment comprises: a first and a second duplexer, a first switch for connecting one of said duplexers to an antenna, a second switch for connecting an output of a transmitter to a first contact or a second contact, a third switch for connecting an input of a receiver to one of two inputs, a first bandpass filter having a first pass band (fA) connected to a first contact of said second switch, a first power amplifier for connecting an output of said first bandpass filter to a first terminal of said first duplexer, a second bandpass filter having a second pass band (fB) connected to a second contact of said second switch, a second power amplifier for connecting an output of said second bandpass filter to a second terminal (B) of said second antenna duplexer, a first front end amplifier for amplifying a signal at a second terminal (B) of said first duplexer, a third bandpass filter having a second pass band (fB) connected to an output of said first front end amplifier, a second front end amplifier for amplifying a signal at a first terminal (A) of said second duplexer, a fourth bandpass filter having a first pass band (fA) connected to an output of said second front end amplifier, means for connecting outputs of said third bandpass filter and said fourth bandpass filter to a first contact (1) and a second contact (2), respectively, of said third switch, a terminal for receiving a control signal for controlling said switches, said power amplifiers and said front end amplifiers, wherein said first and second power amplifiers are controlled so that gain of one of said power amplifiers is zero when the other power amplifier has certain gain, and gain of one of said front end amplifiers is zero when the other front end amplifier has certain gain.

10. A TDMA communication equipment for TDMA communication system according to claim 9, wherein operation of said first switch is carried out by a circulator, and operation of said first and second duplexers is carried out by combination of the first and second bandpass filters.

11. A method for TDMA communication substantially as hereinbefore described with reference to any of the examples described in Figures 6 to 15 of the accompanying drawings.

12. A TDMA communication equipment for TDMA communication system substantially as hereinbefore described with reference to any of the examples described in Figures 6 to 15 of the accompanying drawings.