Multiplex access method

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to a multiple access system for a communication system.

【0002】

[Conventional technology]

In the design of a communication network or system, physical constraints (eg, characteristics of a given communication channel) and system constraints (eg, characteristics of a given communication channel) and system constraints (eg, characteristics of a given communication channel) and system constraints (eg, characteristics of a given communication channel) to allow the network to achieve the desired performance characteristics (eg, reliability of received information). For example, assessing the available bandwidth per channel) is included. The design of wireless communications, especially cellular and microcellular communication networks, is intriguing. Cellular systems in particular require low throughput delays for information, high reliability for information transfer, and high capacitance while limiting the bandwidth of each cellular frequency band.

【0003】

Figure 1 illustrates the components of a cellular or microcellular communication network. Cell 102 represents a portion of the geographic area provided by the system. Within each cell is a base station 105 connected to a payphone network. Base station 105 is a user 1110-i (i = 1, ..., N) who wishes to transmit and receive information (ie, digital data representing text, voice, video, etc.) over a payphone network. ) Has established a wireless link. The wireless link between the user 110-i and the base station 105 is the uplink Ui for transmitting information from the user to the base station 105 and then to the telephone network, and the information received at the base station is transmitted from the telephone network to the user. It consists of a downlink Di for

【0004】

Typically, interest in throughput delays and effective use of bandwidth resources within networks is directed towards the correct design or development of modulation techniques, speech coding methods, channel coding and equalization systems. "Wireless Systems and Technologies: Summary" by JJC Chang, RAMiska and RA Shober, AT & T Tech.J., Vol.72, No.4, pp11-18, July / August 1993, "Movement" by TP Bursh, Jr., etc. Digital Radio for Applications, AT & T Tech.J., Vol.72, No.4, pp19-26, published July / August 1993, and by N, Seshadri, CE.W. Sundberg and V. Weerackody. Advanced Technology for Modulation, Error Correction, Channel Equalization, and Diversity, AT & T Tech.J., Vol.72, No.4, pp48-63, July / August 1993, etc. For example, spatial diversity can be used with some channel coding to minimize delays.

【0005】

Low speed voice encoders such as ADPCM, EDPCM or LD-CELP, as well as modulation methods such as pseudo-analog skewed DPSK are also suitable for reducing delay. T.Miki, C.-EW Sundberg and N. Seshadri, "Pseudo-Analog Speech Transmission in Mobile Wireless Communication Systems," IEEE Trans.Veh.Tech., Vlo42, No1, pp.69-77, published February 1993. reference. Hand width resources are of interest in the design of multiple access systems. The goal of a multiple access system is to coordinate communications for different user pairs within a given cell, such as a finite number of available frequencies, a finite bandwidth per channel, and so on. In particular, the correct design of multiple access systems is important when configuring digital communication networks with low latency and high quality. See, for example, "Digital Cellular Systems in North America" by CE.W.Sundberg and N.Seshadri, GLOBECOM ́90, Vol.1, pp.533-537, San Diego, CA, Dec. 1990.

【0006】

Current wireless networks utilize a multiple access system that multiplexes users together in order to make effective use of network resources. In particular, these networks are TDMA (Time Division Multiple Access) with FDD (Frequency Division Multiple Access), such as Pan-European GSM Systems (Mobile Communications Global Systems) and North American IS-54 Systems, or variants thereof. It utilizes either TDMA / TDD (Time Division Multiplexing), such as digital European cordless telecommunications systems. See "2nd Generation Wireless Information Network" by DJ Goodman, IEEE Trans.Veh.Tech., VT-40, No.2, pp366-374, May 1991.

【0007】

In the multiplex access system described here, a time frame is the basic transmission unit. Each frame is divided into slots for multiple times. As described below, one slot is used for control purposes and another slot is used for information transfer. Slots are assigned to specific users and information is transmitted between slots within the frame. As used herein, the term "information" means data representing audio, text, video or other digital information.

【0008】

Figure 2 illustrates the principle of TDMA / TDD for comparison with other systems. A typical TDMA / TDD has integrated control information in the header of the information sent into the transmitted information slot, but for illustration purposes, frame 201 is all within the same frequency band. It is divided into three parts to be transmitted. The control part contains information related to call management. The uplink portion 210 and the downlink portion 215 are each divided into N slots. Thus, the uplinks and downlinks for each user pair can have guaranteed slots for transmitting information. However, the system capacity is small because the slots are assigned to each user and the slots are reassigned when the user decides not to use the allocated slots.

【0009】

Better utilization of network resources can be achieved if voice users are statistically multiplexed through the use of voice active detection (SAD). FIG. 3 illustrates a TDMA / TDD / SAD format intended for use up to N user pairs. The TDMA / TDD / SAD frame 301 is divided into four parts. Uplink and downlink control parts 305 and 307 include bits for handling call management. The uplink control portion 305 contains a bit for handling a request for the uplink information slot. The downlink control portion 307 includes bits indicating which uplink and downlink information slots have been allocated to send and receive information to the uplink and downlink users. The uplink portion 310 and the downlink portion 315 are similarly divided into slots. Each uplink and downlink portion has the same number of slots, less than N. SAD technology recognizes that one of the characteristic parts of information transfer, especially voice calls, contains unvoiced parts and does not require the transmission of information, that is, it transmits information when N-user pairs are active. Hopefully, not all users are using the slots assigned to them 100% of the time. Therefore, the number of slots required to adequately accommodate up to N user pairs can be significantly reduced by reallocating slots from inactive users to active users. The result is a system with high capacity (because it reduces the number of slots that do not carry information) and low latency (because it reduces the number of slots and shortens the frame). However, the system typically requires that most of the frame be directed to the overhead (ie, the control part). In addition, it becomes an inadequate resource to accommodate all users during peak demand, and information is available due to the lack of available slots for data transmission.

【0010】

Other multiplex access technologies, such as PRMA (Packet Reserved Multiple Access) and R-ALOHA (Reserved ALOHA), recognize the burstiness of voice packets and have a reservation mechanism for time slots to increase system capacity. It is increasing. "Packet Reservation Multiple Access for Local Wireless Communication" by DJ Goodman, RA Valenzuela, KT Gayliard and B. Ramamurthi, IEEE Trans.Comm., COM-37, No.8, pp.885-890, August 1989, by SSLam See "Packet Broadcast Network-Performance Analysis of R-ALOHA Protocol", IEEE Trans.Comm., COM-29, No.7, pp.596-603, July 1980.

【0011】

[Problems to be Solved by the Invention]

However, while these schemes can support a large number of users on the bandwidth of a given channel, these schemes have a limited operating range and, in the case of PRMA, under small delay constraints. Performance is low. In addition, PRMA technology relies on actual voice transmission, that is, the user must actively talk to make slot allocation instead of relying on a separate control mechanism for slot allocation. .. This allocation method leads to collisions between packets of data, which increases delay and throughput. Other systems recognize two types of calls, which often occur when only one user is active, which causes the user when both channels are multiplexed on a common channel. Even if the number of is small, a highly satisfactory multiple gain can be obtained. "Call Transmission Using Compatible Burst Mode Technology" by LMParatz and EV Jones, IEEE Trans.Comm., COM-33, No.6, pp588-591, June 1985, S.Nanda and O.-C "Duplicate Variable Partitions for Wireless Communication" by .Yue, GLOBECOM ́91, pp.32.6.1-32.6.7. However, such systems are typically used to dynamically change the bandwidth allocated to two parties within a single call (dual voice link). This reduces voice quality when both parties talk at the same time or their calls overlap. In addition, it is difficult to allocate management slots because it is necessary to allocate a small number of slots. Therefore, there is a demand for multiple systems for wireless personal communication systems that can provide high capacity, high quality and low latency, comparable to communications, especially wired communications.

【0012】

[Means for solving problems]

The present invention discloses a multiple access scheme in which slots are dynamically allocated between uplink and downlink users. A preferred embodiment shows a method for allocating slots in a communication system adapted for communicating information within allocated slots for uplinks and downlinks between user pairs within N pairs of users. Has been done. This method generates a set of frames, each frame contains an S information slot, and S = U._S + D_S + A, U on the uplink for communication information_S Slots are assigned and on the downlink D for communication information_S Slots are allocated and have unused slots A, provided that A 0. U_S And D_S Changes dynamically to improve the quality and capacity of the entire system.

【0013】

[Example]

FIG. 4 shows a format of the frame 401 that is useful when carrying out the present invention. In the multiple access system of the present invention, called shared time division multiplexing, slots are dynamically allocated between uplinks and downlinks, eg, frame-to-frame-based, and traffic between N-user pairs. It is designed to adjust. Frame 401 is divided into four parts. The call management function is handled by the separate uplink and downlink slots in the uplink control portion 405 and the downlink control portion 407, respectively, as will be described later. The rest of frame 401 is divided into S slots. Where S = U_S + D_S + A and U_S Slots are assigned for uplink information transmission and also D_S Slots are allocated for downlink information transmission. A represents the number of unallocated slots, if any. In frame 401 of FIG. 4, A = 0. The number of slots allocated between the uplink portion 410 and the downlink portion 415 can be varied in each frame as shown in partition 412. However, the total number of voice slots S remains fixed at each frame. If there are a small number of users in the system and the total number of slots in either direction is less than S / 2, the information slots behave like TDD schemes and the S slots are for uplink and downlink access. Equally divided. If the number of users increases and the number of requested voice slots in either direction exceeds S / 2, the partition 412 between the uplink and downlink slots will change as requested.

【0014】

The ability to share a common frequency band contributes to higher static multiple gain, even in narrow band systems with a limited number of users. The value of S is typically 1) the desired quality of information received, that is, what level of packet loss is acceptable, 2) the number of user pairs that are matched, and 3) the voice activity detector, or information. The choice is based on three factors: how much silence and pause in the transfer can be detected. For example, in a system with N = 32 user pairs, standard TDMA / TDD requires 64 voice slots, while TDMA / TDD / SAD requires 46 voice slots with a high quality packet drop rate of 0.01%. Become. STDD typically requires 35 audio slots, assuming a frame size of 2 milliseconds at the same drop rate. The multiple gain of the total statistical is a function of the exact design of the control information.

【0015】

FIG. 5 is a flowchart of the procedure for allocating slots. Here, all signal functions, including channel switching and termination (but typically not the call setup function) associated with calling management in a cellular or microcellular system, communicate via information in the control part. Will be done. In addition, the control information also indicates the state of transmission, that is, whether the user is actively communicating or silent. If the user wants to send information and enters an active state in step 502, for example during a conversation, the state information in the control slot assigned to the user will be the base station, as shown in step 504. Request a slot in the appropriate slot, ie uplink or downlink. Typically, this is done using the FIFO service discipline when allocating information slots to users, but other disciplines, such as random services, are also used. Similarly, the base station recognizes all slot requests originating from the wired end of the network and allocates slots according to step 506. Slot allocation information is carried in the downlink control information slot for both uplink and downlink users. Therefore, in order to reduce the delay, it is advantageous to transmit the uplink control information at a time prior to the transmission of the downlink control information. If the slot is not assigned to the user at the time of the request, the information will be dropped. When the transmission of information is complete, the state information is reset in step 508 and the slot is returned to the pool of unused slots in step 510. The amount of control information is determined by the need for call management functions and the frequency of transmission activity.

【0016】

The use of separate control and information slots helps alleviate the overhead efficiency problems common to PRMA-style networks, and implements a simple access mechanism that favors voice activity detection while providing low access delays. It can be carried out. The uplink control part 405 and the downlink control part 407 each include an N control slot. However, the overhead per frame can be reduced by establishing a duty cycle for the control information. For example, let the total number of control slots be 2C, where C is the number of uplink or downlink control slots and N (N is a multiple of C) is the maximum number of user pairs that can be supported. In general, C <N, and only C user pairs can communicate their control information from and to base stations within a frame period. Therefore, a total K = N / C frame period is required for all users to receive the service by this method. Note that K is a duty cycle that services all users. This access mechanism ensures that all users are guaranteed service within the K-frame period. At the same time, the confirmation is communicated within the same frame period, so that the user with the confirmed reservation can immediately send the voice packet within the same frame. Here, when a user makes a reservation for a voice packet, the user holds the reservation for the minimum K-frame period. For example, if the frame period is 2ms, N = 40, and C = 5, the duty cycle is 8 with a 16ms cycle period. Of course, the longer the duty cycle, the smaller the amount of control overhead information. In STDD, the appropriate cycle period, conveniently synchronized with the voice activity detection rate, is 16 ms.

【0017】

Even in STDD systems, not all information slots may be used, that is, A 0. This spare capacity is used for call setup when a new call arrives in the system. Suppose a new user monitors the control slots for a minimum of one cycle period to check the status of the information slots, that is, to determine if all slots are allocated. The system then uses the spare information slot as a contention channel to notify the base station of this setup request, for example using ALOHA random access. If A (A S) available slots, the new call randomly selects one of these A slots to carry its setup request packet. This request successfully reaches the base station unless another user is transmitting in the same slot. If the total number of currently serviced user pairs is less than N, the new call is successfully serviced and confirmation is sent on the next available downlink control slot. The position of this control slot also determines a new nominal position in the control cycle flow. As mentioned above, when there are few users, STDD behaves like a TDMA / TDD / SAD system in which slots are equally allocated between uplink and downlink. In this case, the spare information slot used to set up the call is treated as an information slot, and as a result is equally allocated until the state requires a partition between the uplink slot and the downlink slot. The slot that was there is moved. The system was described above for up to N user pairs per carrier frequency. The number of carrier frequencies, each carrying up to N user pairs, can be used within the high traffic region.

【0018】

Although the above embodiments have focused primarily on voice communications, STDDs can also be used in mixed traffic conditions, such as one slot carrying data and another slot carrying voice. STDD can also be implemented when the speed per user mode varies, for example in a variable voice quality mode in which a large number of bits are assigned to consumer-demanded video or high quality audio. Control tea obtain contains suitable information. Therefore, this method can be advantageously used when there is high-bandwidth / narrow-band information transfer between users within a user-to-user. Further as an embodiment, the dynamic allocation of slots between the request-based uplink and downlink is frequency division, or pseudo-quadrature, or time, in which information is carried by a dynamically allocated orthogonal code frequency channel. It is carried out in one of the code conversion modes, where the traffic is carried by a direct spectral spread sequence with a mixture of division, frequency division and code division systems. In another embodiment, the STDD format is used in combination with a pseudo-analog skewed DPSK modulation system to further reduce throughput in the communication system.

【0019】

The detailed description above has shown how slots in a frame are dynamically allocated between uplink and downlink users. The method is not limited to any particular hardware or software. Instead, the methods described above show that those skilled in the art could readily apply the hardware or software as available or preferred.

【0020】

[Effect of the invention]

According to the present invention, it is possible to provide a multiplex system for a wireless personal communication system having high capacity and quality and low delay.

[Simple explanation of drawings]

[Figure 1]

It is explanatory drawing which showed the component of the cellular communication system.

[Figure 2]

It is a diagram of the TDMA / TDD frame format known in the prior art.

[Fig. 3]

It is a diagram of the TDMA / TDD / SAD frame format known in the prior art.

[Fig. 4]

It is a diagram of the shared time division duplex frame format used in the present invention.

[Fig. 5]

It is a flowchart of the procedure of allocating a slot in a frame in this invention.

[Explanation of symbols]

102 cells 105 base station 401 frame 405 Uplink control part 407 Downlink control part 410 Uplink part 415 Downlink part