MXPA00004505A - Flexible frequency-time division duplex in radio communications systems - Google Patents

Abstract

A flexible channel architecture supports full-duplex, radio-frequency communication between a base station, such as a PWT or DECT base station, and a group of remote terminals. Downlink communication from the base to the terminals is by way of a first radio-frequency carrier, and uplink communication from the terminals to the base is by way of a first radio-frequency carrier, and uplink communication from the terminals to the base is by way of a second radio-frequency carrier. Each carrier is organized to provide an N-timeslot time-division multiple access data stream (N an integer), so that together the two carriers provide a 2N-timeslot system. Within each frame, data from the base to a terminal is sent on the first carrier during a first time slot, and data from the terminal to the base is sent on the second carrier during a second time slot, the first and second time slots being offset by a time offset which can vary across communications links. The disclosed system provides a unified architecture which allows a single time-division multiple-access hardware platform to efficiently and selectively support either time-division duplex or frequency-division duplex.

Description

DUPLEX OF TIME-FREQUENCY DIVISION FLEXIBLE IN RADIOCOMMUNICATION SYSTEMS FIELD OF THE INVENTION The present invention relates to a radio communication system, and more particularly to duplex schemes in time division multiple access (TDMA) systems. BACKGROUND OF THE INVENTION Most time division multiple access wireless communication systems employ either a time division duplex scheme (TDD) or a frequency division duplex scheme (FDD) to separate upstream and remote transmissions. descending Since both duplex schemes provide certain advantages and disadvantages, both schemes are routinely used in wireless communications applications. For example, in the Personal Wireless Telephony (PWT) standard, time division duplex multiple division time access is used for frequency planning as well as a signal packet and time slot assignment. Such a time division / time division duplex multiple access scheme is suitable for many business wireless communication applications (e.g., small field systems with micro or pico cells). On the other hand, time division multiple access with either time division duplex or frequency division duplex can be preferentially authorized for frequency bands of personal communication service (PCS), depending on the demands of the consumer and of market requirements. In other words, since the structure of a personal communication system is determined primarily by a service provider that has acquired a portion of the frequency spectrum, the technology and frequency usage implemented in that system is ultimately determined by the demands of the consumer as well as legal and practical restrictions. While a first consumer may request a time division division / time division duplex access system for a particular business application, a second consumer may require a frequency division split time / duplex multiple access system for a local circuit application. Therefore, service providers are frequently required to switch between duplex schemes. Conversion between schemes, however, typically results in duplicate effort and therefore significant resources and time are wasted. For example, since conventional time division and frequency division duplex schemes are fundamentally different, it is generally not feasible to use a common hardware platform for both systems. As a result, two development teams are typically assigned, and two different product lines are normally established, to provide the time division and frequency division duplex implementations. Therefore, there is a need for a flexible duplex scheme which allows a communication system adapted to meet the different needs of the consumer without requiring hardware modifications in the hardware architecture of the basic system. COMPENDIUM OF THE INVENTION The present invention satisfies the needs described above and others by providing a flexible division duplex mechanism in time division multiple access communication systems. More specifically, the disclosed system uses a mixed or hybrid duplex splitting mechanism such that the up and down transmissions are frequency-separated while the time segments associated with transmission and reception are also time-separated. The hybrid duplex scheme known in the present invention as time-frequency division duplex (FTDD), allows alternative division duplex mechanisms to be selectively implemented within a communication system without requiring modification of the hardware architecture of the basic system. The time-frequency division duplex system of the present invention provides the advantages of low power consumption and reduction in hardware complexity normally associated with time division / time division multiple access duplex system, while also providing improved interference characteristics by separating the uplink and downlink frequency bands. In addition, the proposed system allows the use of a single hardware platform in multiple technologies and applications. For example, base stations designed for a wireless business system based on time division split / time division multiple access that can also be used, with few changes, for applications in a wireless local circuit (WLL) conventionally based on Time Division / Frequency Division Duplex Multiple Access Technology. Therefore, the embodiments of the invention allow the non-recurring engineering costs typically associated with the development of technology and product to be substantially reduced. As a result, development programs and production cycles for implemented systems can be shortened, and service and product providers can respond more quickly to the customer and to market demand. In accordance with an exemplary embodiment, a base station includes a receiver transmitter configured to transmit downlink communication signals to mobile stations by means of a carrier frequency and receive uplink communication signals from the mobile stations by means of a second frequency carrier, the uplink and downlink communication signals are transmitted and received by means of successive time division multiple access frames, each frame includes a plurality of time segments. For each active communication link between said station and a particular mobile station, a first time segment in each frame is allocated for downlink communication to the particular mobile station and a second time segment in each frame is allocated for link communication ascending from the particular mobile station, the first and second assigned time segments are separated in time by a fixed time offset. Advantageously, the duration of a fixed time deviation may be different for each active communication link (for example: for each established call). For example, where each frame is of duration T and includes 2N time segments, each time segment is of duration T / 2N, the fixed time deviation for each active communication link can be? T = (T / 2N) * m, where m is an integer in the range between 1 to 2N-1. According to an alternative embodiment, a base station includes a transmitter-receiver configured to transmit downlink communication signals to a mobile station by means of a first carrier frequency and receive uplink communication signals from the mobile stations by means of a second carrier frequency , the ascending and descending communication signals are transmitted by means of successive time division multiple access frames, each frame includes a plurality of time segments. Advantageously, a downstream signal processing track and a upstream signal processing track of the transmitter-receiver share the common signal processing components. For example, the shared signal processing components may include one or more of the filters, local oscillator and a modem. The above-described and additional features of the present invention are explained in more detail below with reference to the illustrative examples shown in the accompanying drawings. Those skilled in the art will appreciate that the described embodiments are provided as illustration and understanding and that all equivalent embodiments are contemplated herein. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 presents an exemplary wireless communication system in which the specifications of the present invention can be implemented. Figure 2A shows a base station and a mobile station communicating in accordance with a conventional time division / time division duplex multiple access scheme. Figure 2B presents an exemplary time segment array in a conventional time division / time division duplex multiple access scheme. Figure 3A shows a base station and a mobile station communicating in accordance with a conventional time division / frequency division duplex multiple access scheme. Figure 3B shows an exemplary time segment array in a conventional frequency division / time division duplex multiple access system. Figure 4A shows a base station and a mobile station communicating in accordance with a flexible frequency division duplex time / duplex access scheme in accordance with the present invention. Figure 4B presents an exemplary time segment array in a frequency division duplex time division / duplex access system in accordance with the present invention. Figure 4C presents a time slot arrangement with a flexible frequency division duplex / time division multiple access scheme in accordance with the present invention. Figure 5 is a block diagram of a transceiver constructed in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 presents a wireless communication system 100 in which the specifications of the present invention can be implemented. As shown, the wireless system includes ten Cl-CIO coverage cells or areas, ten Bl-BIO base stations, one TM time master and ten Ml-MIO mobile stations. Said wireless system may be constructed, for example, in accordance with the personal wireless telecommunications (PWT) standard, and may therefore be used, for example, to provide wireless communication within a building or through a field that includes more of ten cells, ten base stations and ten mobile stations; however, ten of each are sufficient for illustration purposes. As shown, one or more base stations may be located in each of the cells. Although Figure 1 shows the base stations located towards the cell centers, each base station can be in place anywhere within the cell. Base stations located towards the cell boundary typically employ directional antennas. The time master TM, or radio switch, maintains the time synchronization between the base stations as is known in the art. The time master can be connected to the base stations by means of cable, radio links or both. Each base station and each mobile station includes a transmitter-receiver for transmitting and receiving communication signals on the air interface. Typically, the base and mobile stations communicate using a time, frequency or multiple code access form (this being, TDMA, FDMA or CDMA) as is known in the art. When mobile stations move within a cell a from cell to cell, communication within at least one base station is always possible. As a result, users of mobile stations can place, receive and make calls anywhere within the coverage area of the total system. To illustrate the features and advantages of the hybrid time-frequency division duplex (FTDD) scheme of the present invention, conventional time division duplex (TDD) and frequency division duplex (FDD) schemes are described below with respect to to Figures 2A, 2B, 3A and 3B. Without losing the generality, the channel definition in the Personal Wireless Telecommunications standard is used to illustrate a conventional time division multiple access (TDMA) / TDD system. Although the channel definition can differ between standards, the following concepts on multiplexing and duplexing remain the same. Figure 2A presents uplink and downlink communication in accordance with a conventional TDD scheme. As shown, the signals transmitted from the TDD base station B20 to a TDD handheld device M20, and those transmitted from a TDD handheld device M20 to a TDD base station B20, are separated in time. If as shown in Figure 2B, a given time interval T represents the duration of a single TDMA / TDD frame T20, then the separation between the uplink and downlink transmissions is typically a means of the predetermined time interval T , that is T / 2. In a Personal Wireless System, each frame lasts 10 milliseconds and includes 24 time segments. Within the data frame, twelve time segments are used for transmission (from the TDD base station B20 to the TDD M20 handheld device), and the remaining twelve time segments are used for reception (this being, the transmission from the TDD M20 hand to TDD base station B20). Although transmissions and receptions are separated by a fixed (or variable) time, they share a common frequency band. The channel of said system is therefore defined by a predetermined frequency and a reference time pair. These TDMA / TDD systems are adopted in several wireless communication applications. An advantage of these systems is that the efficiency of the frequency, since the uplink and downlink transmissions use a common carrier frequency. Additionally, since transmissions and receptions are separated in time, a single hardware track (including filters, local oscillators, etc.) can also be used for both functions. As a result, TDD systems are relatively inexpensive. Also, since the receiving hardware can be turned off during transmissions (and the transmission hardware can be turned off during reception), TDD systems consume relatively little power. By way of contrast, frequency division duplex (FDD) systems require separate frequency bands for uplink and downlink communication. This results from the fact that receive and transmit operations are executed simultaneously in time at different frequencies. A channel of an FDD system is defined by the frequency of operation. Figure 3A shows an upward and downward communication of a conventional FDD base station B30 and an FDD hand-held device M30, and Figure 3B shows an exemplary TDMA / FDD frame T30. Since transmission and reception are carried out simultaneously, separate hardware tracks are required at the base stations and at the terminals. As a result, FDD systems are typically higher cost and consume more power compared to conventional TDD systems. However, FDD systems provide relatively little interference through the channels and are often preferred from an inter-system perspective. In other words, the FDD scheme may be required to make a system compatible with neighboring systems that use an adjacent portion of the frequency spectrum. As a result, FDD systems have been widely adopted in wireless communication applications. Although both TDD and FDD systems provide certain advantages, none is ideally suited for all wireless communication applications. Furthermore, as described above, the fundamental difference between TDD and FDD makes them difficult to adapt to systems configured specifically for one or the other to conform them to a particular application need. Advantageously, the present invention provides a hybrid time-frequency division (FTDD) duplex scheme which provides some of the advantages of both types of conventional systems and which also allows for a single hardware configuration that is easily adapted to satisfy virtually any wireless communication application. To illustrate the FTDD system of the present invention, a TDMA data frame is defined as including 2N time segments (N is an integer) in which N segments are reserved for downlink transmission from a base station to a portable and the N segments The rest are reserved for upstream transmission from a laptop to a base station. Assuming, without losing the generality, that the duration of the time for the ascending and descending segments are "u" and "d", respectively, then the duration T of a single frame is given by: N (d + u) = T. (1) Since the transmission and reception segments are normally of the same duration (being this, d = u), the half of the frame, or T / 2, is normally reserved for downstream transmissions and the remaining half is normally for upstream transmissions. In accordance with the invention, a duplex link is set for frequency and time separation. Specifically, the rising frequency fu is separated from the falling frequency fd by a predetermined frequency deviation Df as follows: fu = fd -? F (2) or fu = fd +? F. (3) Equations (2) and (3) describe the duplex aspect of frequency division of the system. In addition to frequency separation, time separation is also provided. Specifically, the ascending and descending communication between a base station and a portable one are also separated by a fixed time deviation. The specific time deviation is based on a frame length of 2N segments with a period of T / 2N seconds / segment. The time duplex can generally be defined for an ascending packet like Su (t? _) And for the descending packet as SXt ±? T), where ti is defined as the start time for the ascending ^ packet and? T = time deviation = (T / 2N) * m (1 << 2N - 1) (4) (m being an integer which, according to the invention, may be different for each communication link established between a station base and a mobile station). The combined aspects of time division and frequency division of the system can generally be described for the upward packet Su (t?, Fu) and for the downward packet Sd (ti +? T, fU ±? F) or Sd (t? - ? T, fu ±? F). Therefore, according to the invention, the ascending and descending transmissions occur in separate frequencies or in pairs of assigned time segments, a pair of time segments is assigned for each active link between the base station and a mobile station. For each active link, the assigned ascending time segment precedes or follows the corresponding assigned descending segment, within each TDMA frame, by the time offset DT. The time segment coupling is maintained during the link. The selection of uplink and downlink time segments may be based, for example, on a channel selection process which determines the best link arrangement. The determination of the best link arrangement may in turn be based on, for example, an adjacent channel assessment and / or channel interference existing at the time of making the call. Advantageously, either the base station or the mobile station may be responsible for the allocation and selection of the time segment. For example, the base station may select the ascending time segment based on the interference conditions in the base station, while the mobile station selects the descending time segment based on the conditions in the mobile. Alternatively, the base station may select both the uplink and the downlink and its time segments, either independently or by command of the base stations. Note that, because each base station is not limited to a particular portion of the frame for ascending or descending transmissions, a single base station can be used to support laptops through a particular coverage area. In other words, since each segment within each TDMA frame can be assigned either for ascending or descending transmissions, and since the time deviation between a pair of allocated time segments ascending or descending for each active link, a single station The base can communicate with a base station using any available time slot arrangement which may be preferred for the mobile. Of course, a single base station can support at least N duplex links simultaneously (assuming 2N time segments per TDMA frame), and if traffic conditions require it, a second base station can be added in the coverage area to provide full-time spectrum efficiency (this being, both base stations can support 2N simultaneous conversations). Figure 4A presents a base station B40 and an FTDD terminal M40 in communication in accordance with the TDMA / FTDD scheme described above. As shown, Figure 4B presents an exemplary combination of time segment pairs within the TDMA / FTDD data frame T40a for a single base station. Those skilled in the art will appreciate that the combination of pairs in Figure 4B is only one example and that all possible combinations of pairs are contemplated by the invention. In addition, although each pair of uplink and downlink in Figure 4B uses the same time deviation (this being? T = T / 2), those with skill in the subject will realize that each pair can use a different time deviation as is described above. However, assuming for the purpose of illustrating that the pairs of time segments presented are in effect for a first base station, Figure 4C presents a pair of complementary time segments which can be used, for example, by a second station. base without causing interference with the first base station. Together, the first and second base stations provide full-time and spectral efficiency for the coverage area in which they are located (this being, each frequency in each time segment within each TDMA frame is used either for uplink or downlink communication ). In accordance with the invention, proper synchronization of the base station is used to allow a handheld device to carry out communication with any base station in a total system. As is known in the art, said base station synchronization can be implemented by means of a time master TM as presented in Figure 1. In implementations in which the DT time deviation between pairs of ascending time segments or descending in which the time deviation ΔT between pairs of ascending and descending time segments is variable through the communication links (this being, where each active communication link can potentially use a different time deviation), Higher signaling is required between the base stations to implement the deliveries (for example: the information identifying the allocated pair is passed between the base stations during delivery). However, in implementations in which each active link uses a common time deviation? T, the upper signaling can be significantly reduced. See, for example, U.S. Patent Application No., entitled "Radiocommunication Systems with Fixed-Time Duplex Frequency Division" which is hereby incorporated by reference in its entirety. Those skilled in the art will appreciate that the synchronization described above can be obtained by modifying the normal software of existing systems. An exemplary embodiment of the system described above of TDMA / FTDD uses the band definition for the United States Personal Communication Service for ascending and descending frequencies combined with the definition of time division PWT (E). The mode uses a? T = T / 2 fixed for all duplex links and operates with the following parameters:? T = T72 = 5 msec. ? F = 80 MHz: _ T / 2N = 416. 667 μsec Sd (ti ± 5 ms, fu + 8 0 MHz). As indicated above, the TDMS / FTDD scheme of the invention provides, among other advantages, the energy-saving benefits typically associated with conventional TDMS / TDD systems. For example, since the ascending and descending transmissions are separated in time, the disclosed FTDD scheme allows the tracks to be transmitted and received from the transmitter-receiver of the base station or the mobile station are - shared in certain components. This aspect of the invention is presented in Figure 5 In Figure 5, an exemplary base station transceiver 500 includes a transmission signal processing track and a reception signal processing track. As shown, the transmission process track includes a first block and a second transmission block 510, 520, first and second reception and transmission blocks 530, 540, local oscillator 550, a duplexer 560 and an antenna 570. Additionally, the reception signal processing track includes a local oscillator 550, the duplexer 560 and the antenna, as well as a first and a second reception block 580, 590. The first transmission block 510 may include, for example, a conventional converter , and the second transmission block 520 may include, for example, power amplifiers and converters. Additionally, the first reception block 580 may include, for example, low noise amplifiers (LNA) and mixers, and the second reception block 590 may include, for example, a conventional converter and limiter. The first reception / transmission block 530 may include, for example, a modem, and the second reception / transmission block 540 may include, for example, bandpass filters. The duplexer 560 can be, for example, a double-way filter or a switch. During the downlink transmission, the duplexer 560 couples the antenna 570 with the second transmission block 520 and isolates the antenna 570 from the first reception block 580. The baseband transmission signals are processed by the first transmission / reception block 530 and then they are converted, filtered and amplified in blocks 510, 540, 520, respectively, before transmission by means of antenna 570. On the other hand, during up-reception, duplexer 560 couples antenna 570 to the first receiving block 580 and isolates the antenna 570 from the second transmission block 520. The radio frequency signals are received at the antenna 570 and amplified, filtered from the converted blocks 580, 540 and 590, respectively, before being processed by the first block. transmission / reception. Because the transmit reception tracks share certain components (this being, those components in the first and second transmit / receive blocks 530, 540, which are typically very expensive), a base station with transmitter-receiver constructed in accordance with the invention can be made smaller and less expensive compared to conventional TDMA / FDD transceivers. In sum, the present invention features a time division multiple access system that includes a flexible time-frequency division duplex mechanism.

The developed system allows time split division / split time hardware multiple access to be used for applications where duplex frequency bands are required. The system maintains the flexibility of both using the same frequency band or separate bands for up or down communication. In each case, the time division duplex capability is maintained so that the cost of hardware and power consumption are lower. Those skilled in the art will appreciate that the present invention is not limited to the specific exemy embodiments which have been described for the purpose of illustrating the present invention. The scope of the invention, therefore, is defined by the claims which are appended hereto, instead of the foregoing description, and all equivalents which are consistent with the meaning of the claims are within the scope of the invention. the present invention.

Claims (17)

1. CLAIMS A base station for use in a wireless communication system that includes a plurality of mobile stations, said base station comprises: a transmitter-receiver configured to transmit downlink communication signals to said mobile stations by means of a first carrier frequency and receive signals of uplink communication of said mobile stations by means of a second carrier frequency, the uplink and downlink communication signals are transmitted and received by time division multiple access frames, each frame includes a plurality of time segments; wherein, for each active communication link between said base station and a particular mobile station, a first time segment in each frame is allocated for downlink communication to the mobile station and a second time segment in each frame is allocated for uplink communication from the particular mobile station, the first and second time segments are separated in time by a fixed time offset; and where the duration of the fixed time offset can be different for each active communication link.
2. A base station according to Claim 1, wherein each time slice in the multiple time division access frames can be assigned either for uplink communication or downlink communication.
3. A base station claw according to claim 1, wherein said base station is configured to select, for each active communication link, the time segment which is assigned for uplink communication.
4. A base station according to Claim 1, wherein said base station is configured to select, for each active communication link, the time segments which are allocated for up and down communication.
5. A base station according to Claim 1, wherein, for each active communication link, said base station is configured to select, in order of a mobile station, the time segments which are assigned for up and down communication.
6. A base station according to Claim 1, wherein each frame is of a duration T and includes a number, 2N, of time segments, each segment being of a duration T / 2N, and wherein the fixed time deviation for each active communication link is given by? T = (T / 2N) * m, m being an integer in the range between 1 and 2N-1.
7. A wireless communication system, comprising: a plurality of mobile stations; and at least one base station configured to transmit descending communication signals to said mobile stations by means of a first carrier frequency and to receive upward communication signals from said mobile stations by means of a second carrier frequency, the uplink and downlink communication signals. being transmitted and received by means of successive time division multiple access frames, each frame includes a plurality of time segments; wherein, for each active communication link between a particular base station and a particular mobile station, a first time segment frame is assigned for downlink communication from a particular base station to a particular mobile station and a second time segment frame is assigned for uplink communication from a particular mobile station to the particular base station, the first and second assigned time segments being separated by a fixed time offset, and wherein the duration of a fixed time offset may be different for each link of active communication.
8. A communication system according to Claim 7, wherein each time slice in a time division multiple access frame can be assigned for up or down communication.
9. A communication system in accordance with Claim 7, wherein the base stations are configured to select, for each active communication link with a mobile station, the time segments which are assigned for uplink and downlink communication.
10. A communication system according to Claim 7, wherein the mobile stations are configured to select the time segments which are assigned for uplink and downlink communication.
11. A communication system according to Claim 7, wherein the mobile stations are configured to select the assigned time segments for downlink communication and the station is configured to select the allocated time segments for uplink communication.
12. A communication system according to Claim 7, wherein each time division multiple access frame has a duration T and includes a number 2N of time segments, each time segment has a duration T / 2N, and where the fixed time offset for each active communication link between a base station and a mobile station is given by? T = (T / 2N) * m, m being an integer in the range between 1 to 2N-1.
13. A communication system according to claim 7, wherein two base stations are co-located to provide full time and spectrum coverage for a particular system coverage area.
14. A method for carrying out communication between a base station and mobile stations in a wireless communication system, comprising the steps of: transmitting up and down communication signals between the base station and the mobile stations using multiple access frames time, each frame includes a plurality of time segments, wherein the downlink communication signals are transmitted from the base stations to the mobile stations using a first carrier frequency and the uplink communication signals are transmitted from the mobile stations to the base station using a second carrier frequency; and for each active communication link between the base station and a particular mobile station; assigning a first time segment in each frame for descending communication to the particular mobile station; assigning a second time segment in each frame for upward communication from the particular mobile station; and selecting a duration of a fixed time deviation between the first and second assigned time segments.
15. A method according to claim 14, further comprising the step of placing the base station with a second base station similarly constructed to thereby provide full time and spectrum coverage for the mobile stations.
16. 16. A base station for use in a wireless communication system that includes a plurality of mobile stations, said base station comprising: a receiver transmitter configured to transmit downlink communication signals to said mobile stations by means of a first carrier frequency and receiving signals Upward communication of said mobile stations by means of a second carrier frequency, the uplink and downlink communication signals being transmitted and received by time division multiple access frames, each frame includes a plurality of time slots; wherein a downstream signal processing track and an upstream signal processing track of said receiver transmitter share common signal processing components.
17. 17. A base station in accordance with the

    Claim 16, wherein said shared signal processing components include at least one filter, a local oscillator and a modem.

    A base station according to Claim 16, wherein, for each active communication link between said base station and a particular mobile station, a first time segment is allocated in each frame for downlink communication to the particular mobile station and a second The time segment in each frame is assigned for upward communication from the particular mobile station, the first and second assigned time segments are separated in time by a fixed time deviation. A base station according to Claim 18, wherein each time slice in the time division multiple access frames can be assigned either for up or down communication. A base station according to Claim 18, wherein the duration of the fixed time offset may be different for each active communication link. A base station according to Claim 20, wherein each frame is of duration T and includes a number, 2N, of time segments, each time segment being of a duration T / 2N, and wherein the duration of the deviation Fixed time for each active communication link is given by? T = (T / 2N) * m, where m is an integer in the range between 1 and 2N-1. A base station according to Claim 18, wherein the duration of the fixed time offset is the same for each active communication link. A base station according to Claim 22, wherein each frame is of a duration T and includes a number, 2N, of time segments, each time segment being of a duration T / 2N, and wherein the duration of the Fixed time deviation for each active communication link is T / 2.

    SUMMARY OF THE INVENTION ____ A flexible channel architecture supports radiofrequency communication, full duplex between a base station, such as a P T or DECT base station, and a group of remote terminals. A downlink communication from the base to the terminals is made through a first carrier radiofrequency, and an upward communication from the terminals to the base is made through a first carrier radio frequency, and an upward communication from the terminals to the base. base is made through a second carrier radiofrequency. Each carrier frequency is organized to provide a data stream of time division multiple access of N time segments (N is an integer), such that together the two carrier frequencies provide a 2N time slot system. Within each frame, data is sent from the base to a terminal on the first carrier frequency during a first time segment, and data is sent from the terminal to the base on the second carrier frequency for a second time segment, the first The time segment and the second time segment are deviated by a deviation of time that can vary in the communication links. The presented system offers a unified architecture that allows a single time division multiple access equipment platform to efficiently and selectively support either a time division duplex or a frequency division duplex.