Admission policies for integrated voice and data traffic in CDMApacket radio networks

The authors derive optimal admission policies for integrated voice and data traffic in packet radio networks employing code division multiple access (CDMA) with direct-sequence spread spectrum (DS/SS) signaling. The network performance is measured in terms of the average blocking probability of voice calls and the average delay and packet loss probability of data messages. The admission scheme determines the number of newly arrived voice users that are accepted in the network so that the long-term blocking probability of voice calls is minimized. In addition, new data arrivals are rejected if the mean delay or the packet loss probability of data exceeds a desirable prespecified level. A semi-Markov decision process (SMDP) is used to model the system operation. Then, a value iteration algorithm is used to derive the optimal admission control. Two models for the other-user interference of the CDMA system are considered: one based on thresholds and another based on the graceful degradation of the CDMA system performance, and their performance is compared. These admission policies find application in emerging commercial CDMA packet radio networks including cellular networks, personal communication networks, and networks of LEO satellites for global communications     

A Time Reuse Capture Access (TRCA) Protocol for PCS and Wireless ATM Applications

The Time Reuse Capture Access (TRCA) protocol isa medium access control protocol appropriate forpersonal communications and wireless AsynchronousTransfer Mode (ATM) applications. It is based on time reuse rather than frequency reuse. Frequencychannels are reused in every cell (frequency reuse one).Each FDMA channel has a TDMA frame structure. The numberof slots in the frame is equal to the time reuse factor and each slot is assigned to aspecific cell in the reuse cluster. Each mobile usertransmits in its assigned frequency channel and TDMAtime slot which corresponds to the cell it currently belongs. The protocol also exploits the powercapture phenomenon in which simultaneous transmissionsof users in adjacent cells may be successfully received.Two possible applications of the proposed TRCA protocol are considered in this paper. In thefirst application, TRCA is used for random packet accessin wireless personal communication. Users transmit theirpackets using the assigned and non-assigned time slots to take advantage of the effect ofcapture and non-uniform traffic loads. The portion oftransmissions that takes place in each time slot iscontrolled so that the overall throughput is maximized. In the second application, TRCA is used forreliable transmission of ATM cell over a wirelesschannel. The proposed protocol allows the transmissionof continuous bit rate (CBR) ATM cells over a wireless link so that bit error rate (BER) and delayrequirements are met. Transmissions take place in theassigned time slots but the non-assigned time slots canbe used for re-transmission if the previous transmission was unsuccessful.     

Admission control in T/CDMA systems supporting voice and dataapplications

This paper analyses the behavior of two hybrid time-code division multiple-access (T/CDMA) architectures on the up-link of a macrocellular mobile radio system. For the examined schemes two categories of users-voice and data-share the domain of available resources, made up of time slots and codewords, through two alternative assignment strategies. Both solutions attribute voice users one single resource pair, i.e., one time slot and a single code to employ on that time slot, but differ in the way data users requests are accommodated: they are either simultaneously granted several codes over the same time slot or are assigned a single code over several distinct time slots. Call admission control is performed by a channel assignment algorithm which dynamically attributes resources only if specified levels of transmission quality are met on the radio channels. The blocking and the outage probability of the two classes of users are determined and compared, showing that one of the proposed schemes exhibits better performance and allows to satisfyingly serve a significant percentage of data users     

Performance evaluation of a joint CDMA/NC-PRMA protocol forwireless multimedia communications

A joint code division multiple access and noncollision packet reservation multiple access (CDMA/NC-PRMA) technique is proposed and investigated as an uplink protocol for the third-generation (3G) mobile systems. Being the underlying time division multiple access (TDMA) architecture of the CDMA transmissions, NC-PRMA enables the base station (BS) to have a centralized control over the slot allocation policy. In order to reduce the multiple access interference (MAI) variation in a CDMA transmission, two different slot assignment schemes, referred to as load-balancing (LB) and power-grouping (PG) schemes, are proposed and evaluated. Simulation results show that considerable improvement can be achieved over the joint CDMA/PRMA scheme, in which the MAI variation is reduced by way of a dynamic permission probability for contending terminals. Especially when an imperfect power control mechanism is considered, the proposed PG assignment scheme achieves significant performance advantages     

Interaction of TCP and data access control in an integrated voice/data CDMA system

This paper considers the interaction between a proposed data access control scheme and the standardized error recovery schemes on the radio link of a voice/data CDMA system. A data access control scheme for combined voice-data CDMA systems has been proposed and studied in previous literature. The scheme aims to maintain a certain target voice signal to interference ratio (SIR); this is achieved by controlling the data load according to the measured voice SIR. The data users are allowed to transmit in a radio-link time slot with a certain permission probability, which is determined by the base station based on the measured voice SIR in the previous slot. As per the IS-99 standards, however, data transmission operates under the framework of TCP, which is a higher level end-to-end protocol. The TCP data unit, called a segment, is typically equivalent to several tens of physical layer frames; hence, a segment transmission takes up several tens of slots. Due to changes in the number of voice users in talkspurt (which occur on a time scale shorter than a segment transmission time), the slot level data access control scheme can introduce significant variability in the segment transmission time. The effect of such variability on the TCP timers, which operate at the segment level, is of interest. In this paper, an approximate upper bound on the data throughput, taking the presence of TCP into account, is computed. The results provide one with an insight into the interaction of the access control scheme with TCP; they also give practical pointers as to choosing suitable parameters and operating points for the scheme. This revised version was published online in June 2006 with corrections to the Cover Date.     

Bandwidth guaranteed call admission in TDMA/CDMA ad hoc wireless networks

This paper first studied the timeslot assignment problem in time division multiple access/code division multiple access (TDMA/CDMA) wireless ad hoc networks. Given a path P, we prove that a timeslot assignment providing one unit of bandwidth on P can be found in O(P) time if such an assignment exists. The results have been extended to the case that P can provide two units of bandwidth. Based on the timeslot assignment for the special cases, an efficient slot assignment algorithm with O(P²k) is proposed for general cases, where k is the number of slots in a TDMA frame. Then, the timeslot assignment algorithm is integrated into a quality of service (QoS) call admission scheme for QoS call requests. Extensive simulations are conducted and the results have demonstrated the superior performance of our method.     

High data-rate packet communications for cellular networks usingCDMA: algorithms and performance

The advantages of code division multiple access (CDMA) for cellular voice have become well known, and IS-95-based systems have now been widely deployed. Attention is now focused on higher data-rate packet services for cellular systems. Although many packet multiple access schemes have been studied over the years, researchers have often studied single cell performance and ignored reuse. Moreover, direct sequence spread spectrum (DSSS) has been considered unsuitable for high data-rate packet multiple access since spreading limits the permitted data rates, DSSS requires large overhead (preambles) for acquisition and requires closed-loop power control. In this paper, we describe a scheme for high data-rate packet service using CDMA that addresses all of the above problems and has been standardized in Revision B of IS-95. A low rate fundamental code channel is maintained that eliminates the need for long preamble and provides closed-loop power control. Reuse is managed by the infrastructure through a “burst-level” admission control based on load and interference-level measurements at the base stations and mobiles. We report on the feasibility of such a burst-mode packet data service for cellular CDMA networks. The focus is not only on the performance of high data-rate users, but also on the impact on voice users sharing the CDMA band. We propose a multitiered performance analysis methodology consisting of a mix of static simulations, dynamic simulations at different time scales, and analytic methods to address the various feasibility issues: impact on coverage; capacity; power control; and effectiveness of burst admission algorithms. Based on the current study, we can conclude that the proposed approach is well suited for third-generation wideband CDMA systems being considered for standardization throughout the world     

一种基于CDMA/TDMA混合多址的GSM与CDMA扩容方法

提出了一种基于CDMA/TDMA混合多址的GSM与CDMA扩容方法。在发送端,通过扩频码对GSM信号进行直接序列扩频,使其多址方式由TDMA变换为CDMA/TDMA,然后与CDMA信号在空间同频传输,这样就可以解决两个系统在Um接口的兼容问题;在接收端,使用相同的扩频码对CDMA/TDMA信号进行解扩,使其多址方式由CDMA/TDMA还原为TDMA,由此可以将GSM与CDMA两种信号进行分离。文章提出了用互补码集作为多址接入码,并给出了一个时隙内GSM用户被扩频调制的具体过程。理论分析和仿真结果表明,该方法可使系统总容量扩大2倍。     

Network Control for Multibeam TDMA and SS/TDMA

This paper concentrates on the control of individual burst transmissions of traffic and reference stations in TDMA and SS/ TDMA networks. In a TDMA system, the principal task of a TDMA terminal is to transmit each burst at the proper time to assure that, at the satellite, the burst resides in its assigned location in the TDMA frame. The composite of assigned positions for all bursts in the TDMA frame, or frames if more than one transponder is involved, is called the burst time plan. The paper discusses a specific concept of control used by a station to acquire and synchronize its burst transmission to assigned time slot(s) in the TDMA frame. The concept is applied to single-beam (global or regional) and muitibeam systems. The method used controls the instant of traffic burst transmission by introducing a time delay at each station which causes the round-trip propagation time between the satellite and all earth stations to be equal for burst position control purposes. This time delay is simple to implement in the TDMA terminal's timing circuitry and does not require the storage of traffic to accomplish it. It is also shown that the control method leads to a simple means for accomplishing synchronous burst time plan changes throughout the network. The functions of the reference stations needed to accomplish the burst time plan control are defined and explained. The discussion extends to SS/TDMA, and explains how the satellite switch state time plan change can be synchronized to the overall network burst time plan change.     

A Medium Access Control Protocol for Voice/Data Integrated Wireless CDMA Systems

In this paper, a medium access control protocol is proposed for integrated voice and data services in wireless local networks. Uplink channels for the proposed protocol are composed of time slots with multiple spreading codes per slot based on slotted code division multiple access (CDMA) systems. The proposed protocol uses spreading code sensing and reservation schemes. This protocol gives higher access priority to delay‐sensitive voice traffic than to data traffic. The voice terminal reserves an available spreading code to transmit multiple voice packets during a talkspurt. On the other hand, the data terminal transmits a packet without making a reservation over one of the available spreading codes that are not used by voice terminals. In this protocol, voice packets do not come into collision with data packets. The numerical results show that this protocol can increase the system capacity for voice service by applying the reservation scheme. The performance for data traffic will decrease in the case of high voice traffic load because of its low access priority. But it shows that the data traffic performance can be increased in proportion to the number of spreading codes.     

Performance evaluation of a satellite-switched variable-frame TDMA system

In satellite-switched time-division multiple access (SS/TDMA) systems, the demand assignment control is a suitable scheme for the bursty packets to enhance the capacity efficiency. In the system, by applying the demand assignment scheme, the minimum transmission time could be achieved by the efficient time slot assignment algorithm. According to a given traffic matrix, the minimum transmission time cannot exceed the fixed TDMA frame duration. The spare time may be left at the end of the TDMA frame as the growth space for the future needs. To increase the system efficiency, the spare time could be reduced. In this paper, a demand assignment protocol with a variable frame is proposed for the system. The Markov chain model is applied to analyze the system performance on throughput, balking probability and packet delay. Performance comparison with the previous presented protocol, the proposed protocol could show a simple control technique and the efficient performance results in the system. It is a suitable candidate to be employed in the satellite networks to provide communication between the satellite and earth stations.     

Reduced‐frame TDMA protocols for wireless sensor networks

Time‐division multiple‐access (TDMA) is a common medium access control paradigm in wireless sensor networks. However, in its traditional form, the TDMA‐based protocols suffer from low channel utilization and high message delay because of a long frame length needed to provide collision‐free transmissions, which is particularly damaging in dense wireless sensor networks. In this paper, we investigate the performance and the energy efficiency of a class of TDMA‐based protocols, called reduced‐frame TDMA, where every TDMA slot is augmented with a short time period dedicated for carrier sense multiple access‐based contention resolution mechanism. Because of their ability to dynamically resolve collisions caused by conflicting slot assignments, the reduced‐frame TDMA protocols can be configured with any frame length, independently of node density. In addition, we present a distributed heuristic slot assignment algorithm that minimizes interslot interference in the presence of limited number of slots per frame. The simulation results indicate that the reduced‐frame TDMA protocols significantly reduce the message delay and increase the maximum throughput without incurring significant penalty in energy efficiency compared with the traditional TDMA scheme. Copyright © 2012 John Wiley & Sons, Ltd.     

A Bandwidth Reservation Multiple Access Protocol for Wireless ATM Local Networks

A bandwidth reservation multiple access scheme(BRMA) is proposed to resolve contention and assignbandwidth among multiple users trying to gain access toa common channel such as in mobile users contending for resources in an ATM-based cellular networkor a wireless local area network (LAN) with shortpropagation delays. The protocol is best suited tosupport variable-bit-rate (VBR) traffic that exhibits high temporal fluctuations. Each mobile user isconnected end-to-end to another user over virtualchannels via the base station that is connected to thewired ATM B-ISDN network. The channel capacity is modeled as a time frame with a fixed duration.Each frame starts with minislots, to resolve contentionand reserve bandwidth, followed by data-transmissionslots. Every contending user places a request for data slots in one of the minislots. If therequest is granted by the base station through adownlink broadcast channel, the user then startstransmission in the assigned slot(s). The number ofassigned slots varies according to the required qualityof service (QoS), such as delay and packet lossprobability. A speech activity detector is utilized inorder to indicate the talkspurts to avoid wastingbandwidth. Due to its asynchronous nature, BRMA is ratherinsensitive to the burstiness of the traffic. Since theassignment of the minislots is deterministic, therequest channels are contention-free and the data channels are collision-free. Hence, in spite ofthe overhead (minislots) in each frame, BRMA provideshigher throughput than Packet Reservation MultipleAccess (PRMA) for the same QoS, especially for high-speed systems. A better delay performance is alsoachieved for data traffic compared to Slotted Alohareservation-type protocol PRMA. In addition, BRMAperforms better in terms of bandwidth efficiency thanthe conventional TDMA or the Dynamic TDMA, wherespeech activity detectors are very difficult toimplement.     

The impact of space division multiplexing on resource allocation: a unified treatment of TDMA, OFDMA and CDMA

Space division multiple access (SDMA) with an antenna array at the transmitter is a promising means for increasing system capacity and supporting rate-demanding services. However, the presence of an antenna array at the physical layer raises significant issues at higher layers. In this paper, we attempt to capture the impact of SDMA on access layer channel allocation, reflected on channel reuse. This impact obtains different twists in TDMA, CDMA and OFDMA due to the different nature of co-channel and cross-channel interference and the different interaction of user spatial channel characteristics with system channels, namely time slots, codes and subcarriers. We consider these access schemes in a generalized unified framework and propose heuristic algorithms for channel allocation, downlink beamforming and transmit power control so as to increase total provisioned system rate and provide QoS to users in the form of minimum rate guarantees. We study the class of greedy algorithms that rely on criteria such as induced or received interference and signal-to-interference ratio (SIR), and a class of SIR balancing algorithms. Results show superior performance for SIR balancing resource allocation and expose the performance benefits of cross-layer design.     

Adaptive admission/congestion control policies for CDMA‐based wireless internet

Radio resource management (RRM) is vital for the next generation wireless networks. RRM comprises many functionalities and this paper focuses on the investigation of the performance of several adaptive call admission/congestion control policies based on a window‐measurement estimation of the status of the buffer at the base station under the hybrid TDMA/CDMA access scheme. In our study, we interrelate the physical limitations of the base stations (i.e. the number of transmission and reception modems), call and burst level traffic, instantaneous buffer conditions and end‐to‐end bit error performance in one queuing problem. Subsequently, a window‐measurement estimator is implemented to estimate the likelihood of buffer congestion at the base station. Accordingly, the traffic loads shall be controlled. We use event‐driven simulation to simulate the multimedia integrated CDMA networks where heterogeneous traffic users are multiplexed into a simple TDMA frames. The simulation results show outstanding performance of the proposed call admission/congestion control policies in guaranteeing QoS requirements. Copyright © 2005 John Wiley & Sons, Ltd.     

Performance Evaluation of an Integrated Access Scheme in a Satellite Communication Channel

A method for realizing a circuit and packet integrated access scheme in a satellite communication channel is considered. Two kinds of terminals are assumed, namely, bursty terminals for handling bursty traffic and heavily loaded terminals for long-holdingtime message traffic. In this method, the channel frame is divided into two subframes: one is for bursty terminals, and the other is for heavily loaded terminals. The subframe for heavily loaded terminals is further divided into two subchannels, a reservation subchannel (consisting of small slots) and a message subchannel. The bursty terminals transmit their packets in their dedicated subframes on the slotted ALOHA protocol. The heavily loaded terminal having a message transmits, first of all, a reservation packet in a randomly selected small slot of the reservation subchannel to reserve slots in the coming message subchannels. One slot in the same position of each of the succeeding message subchannels is reserved for the terminal until the end-of-use flag, transmitted from the terminal, is received by the satellite. Mean transmission delays for both kinds of traffic in this method are analytically obtained. We show that there exists an optimal frame length which minimizes mean transmission delay for one kind of traffic while keeping mean transmission delay for the other kind under some permissible value.     

Delay and throughput characteristics of TH, CDMA, TDMA, and hybridnetworks for multipath faded data transmission channels

The new concepts of adaptive time hopping and variable frame code division (CDMA) multiple access are introduced. By a unified analysis, the probabilities of bit and packet errors in multipath fading environment for five time division (TDMA), code division, and time hopping (TH) related multiaccess networks are obtained; namely, TDMA, CDMA, CDMA/TDMA, Adaptive CDMA/TH, and variable frame CDMA/TDMA networks. The delay and useful throughputs of the five systems are also evaluated for data and voice traffic. All systems compared have the same channel power and bandwidth and support the same traffic. Though implementation issues are not covered, CDMA systems are put at a disadvantage (compared to cellular-type FDMA networks, for example) by ignoring such inherent advantages as voice silence utilizations and automatic frequency reuse. Nontheless, two CDMA systems outperform TDMA systems at low and medium input traffics     

Efficiency of the GSM-GPRS Air Interface for Real-Time IP Traffic Flows With and Without Packet Dropping

One IP terminal can occupy a single slot or a multiple number of slots within time frames in the GSM and GPRS, respectively. A limited number of radio resources (slots) are allocated in a base station for such IP terminals. If one IP terminal can occupy only one slot discontinuously in a time frame, there is one possibility resorting to all IP terminals to preserve active mode at a time. Thus, the number of accepted call in the GSM is the same as that of the radio resource. Similarly, if one terminal can occupy a multiple number of slots discontinuously/dynamically in a time frame, the number of accepted calls is obtained by dividing the number of radio resources during that time by the maximum allowed number of slots per IP terminal. A burstiness factor is defined for the IP traffic over GSM-GPRS air interface. Traffic channel efficiency with a bursty real-time IP traffic is unacceptably low, especially with the range of acceptable call loss probabilities pertaining to a lower burstiness factor. The channel efficiency can be enhanced and the call loss probability can be suppressed significantly if a higher maximum number of calls is accepted. Allocated radio resources are less than the maximum number of packet transmissions at a time. Therefore, some packets could be dropped from the real-time transmission system. A complete analysis for the real-time IP packet transmission over the single slot GSM and dynamically variable multislot GPRS air interface without packet dropping, and with packet dropping that increases the channel efficiency is executed. Results show that the channel efficiency as well as the packet dropping probability increases with increasing call intensity, maximum number of admitted IP calls and the burstiness factor.     

采用TDMA和CSMA混合MAC协议的时隙调整算法

由于车联网(VANET)拓扑动态变化,车辆高速移动以及不同服务质量要求,制定媒体接入控制(MAC)协议面临巨大挑战。在控制信道间隔内采用基于TDMA和CSMA的混合接入协议是最有效的MAC协议之一。基于TDMA和CSMA的混合MAC协议(T-C-MAC)能够依据车辆环境调整TDMA帧长度,并能有效地传输非安全消息。为了提高T-C-MAC协议的性能,提出了一种基于三跳邻居信息的时隙调整(THSA) 算法。通过有效地调整车辆传输时隙,基于THSA的MAC（THSA-MAC）协议能够有效地实施广播服务,提高了安全消息传输率。实验数据表明,THSA-MAC有效地提高了安全消息传递率。     

Performance of a Dynamic TDMA System for Mobile Wireless Access

A dynamic TDMA system can utilize voice activityand allow the integration of voice and data traffic.This can be achieved by allocating frequency channelsand time slots on demand. In this approach, upon the arrival of a talkspurt or a data packet,the base station is requested to assign a time slot foreach transmission. Message requests and assignments ofmobile users are carried over a Control channel, while the voice and traffic are transmittedover a Traffic channel. Time slot assignments are madefrom a pool of Traffic channels. A numberof slots in the pool will be shared by voice and data, with voice having priority over data, andthe remaining will be used by data only. Voice slots arereserved for the duration of the talkspurt whereas datapackets are assigned on a per-slot basis. Data packets can be buffered whereas voicetraffic can only tolerate limited delay beyond whichtalkspurts will be clipped off. The Control channeluplink access is based on Slotted Aloha so that mobile users have autonomous access to base stations.This paper presents the performance of the dynamic TDMAsystem outlined here. The analysis aims at assessing thecapacity gained by using voice activity and voice/data integration, in terms of theimpairments introduced to voice quality (e.g., speechclipping and/or delay) and the delays to data packets.The analysis has been based on a discrete time Markov model operating on a frame-by-frame basis thatprovides the joint distribution of the number of activevoice and data users in the system. The analysis alsoevaluates the delays of message requests via the uplink control channel. In evaluating theclipping probability, we combine the impact of both theaccess delays at the control channel as well as theunavailability of time slots in the pool. Performance results indicate that the capacity gain mayexceed 80% and the speech clipping can be kept below 1%.Also, data packets may be transmitted with limiteddelays even when all capacity is allocated for voice users. The proposed approach may be used toenhance the capacity of the existing TDMA cellularsystems and to provide integration of voice and dataservices.