A spread slotted CDMA/ALOHA system with hybrid ARQ for satellitemultiple access

We propose and investigate a new type of satellite multiple access protocol that combines the characteristics of the spread slotted (SS)-ALOHA protocol, code division multiple access (CDMA), and the hybrid automatic repeat request (ARQ) error controlling and retransmission scheme, in order to increase the throughput by reducing the number of retransmissions and to keep the bit error rate (BER) of the satellite link low when the channel experiences heavy traffic. The main feature of our proposed system is the utilization of two different fields in the analysis of the satellite multiple access problem. Since the hub now possesses the forward error correction (FEC) capability to correct errors that appear after the CDMA despreading of the packets, the satellite does not need to ask so often for the retransmission of erroneous packets and will ask for retransmission only when the FEC error correcting capability is exceeded. This paper also presents the adaptive optimization of the balance between the CDMA processing gain and FEC coding gain in order to obtain a better throughput for the SS-CDMA/ALOHA with hybrid ARQ protocol for satellite multiple access. The optimization is made with the constraint of keeping the bandwidth of the transmitted packets constant during all times. According to this, the effective throughput of the protocol (information bits over total transmitted bits ratio) is improved by adaptively changing the CDMA and FEC codes used in the transmission. This adaptive optimization is done by observing the channel status or load and increasing or decreasing both coding schemes' gains. Computer simulations show the performance of the proposed multiple access scheme     

Dynamic reservation TDMA protocol for wireless ATM networks

A dynamic reservation time division multiple access (DR-TDMA) control protocol that extends the capabilities of asynchronous transfer mode (ATM) networks over the wireless channel is proposed in this paper. DR-TDMA combines the advantages of distributed access and centralized control for transporting constant bit rate (CBR), variable bit rate (VBR), and available bit rate (ABR) traffic efficiently over a wireless channel. The contention slots access for reservation requests is governed by the framed pseudo-Bayesian priority (FPBP) Aloha protocol that provides different access priorities to the control packets in order to improve the quality-of-service (QoS) offered to time sensitive connections. DR-TDMA also features a novel integrated resource allocation algorithm that efficiently schedules terminals' reserved access to the wireless ATM channel by considering their requested bandwidth and QoS. Integration of CBR, voice, VBR, data, and control traffic over the wireless ATM channel using the proposed DR-TDMA protocol is considered in this paper. Simulation results are presented to show that the protocol respects the required QoS of each traffic category while providing a highly efficient utilization of approximately 96% for the wireless ATM channel     

TDMA+TDD系统中高速无线数据传输的实现

针对浮空平台搭载的载荷重量、体积、功耗受限的问题,提出了一种时分多址结合时分双工的通信模式。使用该通信模式,网内所有节点均工作于一个频率之上,只需配备一套收发通道,解决了浮空平台载荷受限的问题。在此基础上,通过软硬件设计,实现了该通信系统的信号收发流程、帧协议和参数设置,并构造出一套完整的通信系统。仿真实验和实测结果表明,利用该方案构造出的通信系统较传统的频分多址通信方式在体积、重量、成本等方面均有优势,更适用于浮空平台的远距离、高码率传输。     

Adaptive minimum-BER linear multiuser detection for DS-CDMA signalsin multipath channels

The problem of constructing adaptive minimum bit error rate (MBER) linear multiuser detectors is considered for direct-sequence code division multiple access (DS-CDMA) signals transmitted through multipath channels. Based on the approach of kernel density estimation for approximating the bit error rate (BER) from training data, a least mean squares (LMS) style stochastic gradient adaptive algorithm is developed for training linear multiuser detectors. Computer simulation is used to study the convergence speed and steady-state BER misadjustment of this adaptive MBER linear multiuser detector, and the results show that it outperforms an existing LMS-style adaptive MBER algorithm presented by Yeh et al. (see Proc. Globecom, Sydney, Australia, p.3590-95, 1998)     

High-quality audio transform coding at 64 kbps

This paper presents a transform coding algorithm devoted to high quality audio coding at a bit rate of 64 kbps per monophonic channel. It enables the transmission of a high quality stereo sound through the basic access (2B channels) of ISDN. Although a complete system including framing, synchronization and error correction has been developed, only the bit rate compression algorithm is described here. A detailed analysis of the signal processing techniques such as the time/frequency transformation, the pre-echo reduction by adaptive filtering, the fast algorithm computations, etc., is provided. The use of psychoacoustical properties is also precisely reported. Finally, some subjective evaluation results and one real time implementation of the coder using the ATT DSP32C digital signal processor are presented     

基于TDD-CDMA的集成可变速率多媒体业务传输的MAC协议

文章给出了一种应用于移动多媒体通信的无线媒体接入控制(MAC)协议.该MAC协议采用混合TDMA/CDMA结构,以提高资源利用率;采用多码并行传榆提供可变速率,以支持集成多媒体业务.系统仿真表明,该协议具有较高的码利用率和良好的灵活性,适用于可变速率多媒体业务集成传输.     

基于天线波束成形的OFDMA系统的自适应资源分配

对正交频分复用接入系统在多用户多天线传输情况下的自适应资源分配策略进行了研究,提出了一种基于天线波束成形的,包括动态子载波分配、自适应调制、比特加载的无线资源分配方案.算法的优化设计目标是在满足总的恒定传输比特数和误比特率性能要求的情况下,使得系统总的发射功率最小.仿真结果表明,由于多天线阵列增益和多用户分集增益,系统整体性能得到了明显的优化.     

Integrated video and voice transmission using packet reservation multiple access

This paper proposes a new protocol for the integration of voice and video transmission over the packet reservation multiple access (PRMA) system that is a modification of reservation‐ALOHA protocol. We focus on low bit‐rate video applications like video conferencing and visual telephony for wireless communications. The ITU–T H.263 standard provides a solution to the need for low bit‐rate video compression under 64 kbytes/s. The proposed protocol assumes that each voice terminal follows a traffic pattern of talk spurts and silent gaps with fixed permission probability (p=0.3), and each video terminal has the higher permission probability (p=1) to access the available slot based on ITU–T H.263 standard. Again, we present a ‘pseudo‐reservation’ scheme to release slots reserved by video terminals according to the contents of each video transmission buffer, and the active voice terminals can temporarily access the additional slots to improve the performance without sacrificing the video capacity of the system. The packet dropping probability of the active voice terminals and bandwidth utilization of the system are superior to the original PRMA, as indicated in simulation results. Copyright © 2001 John Wiley & Sons, Ltd.     

Achievable QoS in an interference/resource limited shared wirelesschannel

In this work, the region of achievable quality-of-service (QoS) is precisely described for a system of real-time heterogeneous variable bit rate (VBR) sources competing for slots (packet transmission times) of a time division multiple access (TDMA) frame. The QoS for each application is defined in terms of a maximum tolerable packet-dropping probability. Packets may be dropped due to delay violations and channel induced errors. The region of achievable QoS is precisely described for an interference/resource limited network by considering the underlying TDMA-multiple access control (TDMA-MAC) structure and the physical channel. A simple QoS-sensitive error-control protocol that combats the effects of the wireless channel while satisfying the real-time requirements is proposed and its impact on the region of achievable QoS is evaluated. The results presented here clearly illustrate the negative impact of a poor channel and the positive impact of the employed error-control protocol on the achievable QoS. The region of achievable QoS vectors is central to the call admission problem, and in this work, it is used to identify a class of scheduling policies capable of delivering any achievable performance     

Multitone spread spectrum multiple access communications system ina multipath Rician fading channel

The paper proposes a new multiple access communications system based on the combination of multitone transmission and direct sequence spectrum spreading (DS/SS). Multitone transmission is proposed because the associated larger symbol duration is favorable to combat the effects of multipath propagation. The multiple access capability of the system is achieved by means of DS/SS which also helps to combat the presence of several paths. On the other hand, DS/SS is also attractive to decrease the multiple access interference. The performance of this system is investigated for a multipath, slowly Rician fading and frequency selective channel, and a suboptimal receiver based on matched filters. The multiple access interference is also taken into account, A model for the computation of the bit error probability is derived for QPSK modulation of the orthogonal tones by the spread symbols. The system performance is investigated for selection diversity and maximal ratio combining (RAKE reception). Then the influence of the number of tones is investigated for given bandwidth, bit rate and transmission power. The positive effect of a multitone spread spectrum transmission is demonstrated     

QoS-oriented packet scheduling for wireless multimedia CDMA communications

In the third-generation (and beyond) wireless communication systems, there will be a mixture of different traffic classes, each having its own transmission rate characteristics and quality-of-service (QoS) requirements. In this paper, a QoS-oriented medium access control (MAC) protocol with fair packet loss sharing (FPLS) scheduling is proposed for wireless code-division multiple access (CDMA) communications. The QoS parameters under consideration are the transmission bit error rate (BER), packet loss, and delay requirements. The MAC protocol exploits both time-division and code-division statistical multiplexing. The BER requirements are guaranteed by properly arranging simultaneous packet transmissions and controlling there transmit power levels, whereas the packet loss and delay requirements are guaranteed by proper packet scheduling. The basic idea of FPLS is to schedule the transmission of multimedia packets in such a way that all the users have a fair share of packet loss according to their QoS requirements, which maximizes the number of the served users under the QoS constraints. Simulation results demonstrate effectiveness of the FPLS scheduler, in comparison with other previously proposed scheduling algorithms.     

移动Ad HOc网络中的公平按需多址接入协议

基于快速、有效竞争预约接入、无冲突轮询传输的思想和带冲突预防的冲突分解策略,本文提出了适于移动Ad Hoc网络的公平按需多址接入(FODA)协议.该协议在分群结构的基础上,利用公平冲突预防算法预约信道资源获得轮询服务,从而完全消除了载波侦听方式下多跳无线网络业务传输中的隐藏终端和暴露终端问题.另外,公平冲突预防算法解决了节点竞争接入时的冲突问题和不公平现象.最后,仿真结果表明,与带冲突避免的载波侦听多址接入(CSMA/CA)和轮询协议相比,FODA协议可以提供较高的信道吞吐量、较低的平均消息丢弃率和平均消息时延.     

Multiple access capacity of UWB m-ary impulse radio systems with antenna array

In this paper, the multiple access capacity of an Mary pulse position modulation (PPM) impulse radio (IR) system with antenna array is analyzed in dense multipath environments. An antenna array with Rake receivers is used to capture the signal energy from multipaths. Multiple access performance of the system is evaluated in terms of number of supported users for a given bit error rate and bit transmission rate with different number of antenna elements and selected paths. Numerical results show that the multiple access capacity of an M-ary IR system can be improved significantly by increasing the number of antenna elements and/or by adding more paths coherently at the receiver.     

An OFDM-TDMA/SA MAC Protocol with QoS Constraints for Broadband Wireless LANs

Orthogonal frequency division multiplexing (OFDM) is an important technique to support high speed transmission of broadband traffic in wireless networks, especially broadband wireless local area networks (LANs). Based on OFDM, a new multiple access scheme, called OFDM-TDMA with subcarrier allocation (OFDM-TDMA/SA), is proposed in this paper. It provides more flexibility in resource allocation than other multiple access schemes such as OFDM-TDMA, OFDM-frequency division multiple access (OFDM-FDMA), and orthogonal frequency division multiple access (OFDMA). With OFDM-TDMA/SA, a medium access control (MAC) is designed for broadband wireless LANs. It optimizes bit allocation in subcarriers so that maximum bits are transmitted in each OFDM symbol under a frequency selective fading environment. The OFDM-TDMA/SA MAC protocol also supports three classes of traffic such as guaranteed, controlled-load, and best effort services. Based on the optimum subcarrier bit-allocation algorithm and considering heterogeneous QoS constraints of multimedia traffic, a hierarchical scheduling scheme is proposed to determine the subcarriers and time slots in which a mobile terminal can transmit packets. In such a way, the OFDM-TDMA/SA MAC protocol significantly increases system throughput in a frequency selective fading environment and guarantees QoS of multimedia traffic. Computer simulation is carried out to evaluate the performance of the OFDM-TDMA/SA MAC protocol. Results show that the new MAC protocol outperforms other MAC protocols for OFDM-based wireless LANs. This work was supported by the State of Georgia Yamacraw Project (E21-105).     

Single and multiple cell deployment of adaptive antennas with CDMA

The issue of multiple cell deployment of adaptive antennas for a direct sequence code division multiple access (DS-CDMA) system is investigated. The approximate formulas for the signal-to-interference gain and the bit error rate are extended, using the method of the effective radiation pattern characteristics, produced with an adaptive antenna in a real environment. (The word effective implies that the value for the parameter under discussion is what can be achieved if the scattering and signal mismatching effects are considered.) The presented formulas are then used to study the different options for the deployment of adaptive antennas in a multi-tier DS-CDMA system     

Capacity analysis of reservation-based random access for broadband wireless access networks

In this paper we propose a novel model for the capacity analysis on the reservation-based random multiple access system, which can be applied to the medium access control protocol of the emerging WiMAX technology. In such a wireless broadband access system, in order to support QoS, the channel time is divided into consecutive frames, where each frame consists of some consequent mini-slots for the transmission of requests, used for the bandwidth reservation, and consequent slots for the actual data packet transmission. Three main outcomes are obtained: first, the upper and lower bounds of the capacity are derived for the considered system. Second, we found through the mathematical analysis that the transmission rate of reservationbased multiple access protocol is maximized, when the ratio between the number of mini-slots and that of the slots per frame is equal to the reciprocal of the random multiple access algorithm?s transmission rate. Third, in the case of WiMAX networks with a large number of subscribers, our analysis takes into account both the capacity and the mean packet delay criteria and suggests to keep such a ratio constant and independent of application-level data traffic arrival rate.     

Interference‐resistant cooperative wireless networks based on complementary codes

Spatial diversity in wireless networks can be attained by exploiting the broadcast nature of wireless transmission without the need of multiple antennas in individual device, leading to the implementation of cooperative communication. While most prior works focused on the single source—destination scenario, it should be more realistic to consider how to induce cooperation among multiple source‐destination pairs assisted by multiple relays. In such a case, multiple access interference (MAI) may present due to asynchronous transmissions of the users and relays. In this paper, a cooperative network architecture based on orthogonal complementary (OC) codes inherently immune to MAI is proposed. To efficiently utilize the scarce radio spectrum and codes, a centralized medium access control (MAC) protocol is proposed to coordinate the code assignment and channel access among users and relays. We theoretically analyze the bit error rate (BER) performance of the proposed OC coded cooperative network over multipath Rayleigh fading channel. The performance gain resulted from different numbers of relays is investigated, and compared with a time division multiple access (TDMA) based cooperative scheme. We show that the proposed OC coded cooperative network performs well in the presence of timing offset, and thus is well suited for asynchronous uplink transmission with cooperative relaying. Copyright © 2009 John Wiley & Sons, Ltd.     

Demonstration of 20 Gbit/s subcarrier multiplexed transmissionsystem

A 20 Gbit/s subcarrier multiplexed (SCM) optical transmission system is presented. To date, this represents the highest aggregate bit rate SCM transmission that has been demonstrated. Results show that the bit error rate (BER) is less than 10^-12 for a link loss of 29.5 dB, which corresponds to 118 km single mode fibre (SMF). Furthermore, excellent performance is demonstrated after transmission over 82 km of dispersion compensated SMF. Results suggest that the system can support transmission over multiple spans of optical fibre     

A multi-layer collision resolution multiple access protocol for wireless networks

In mobile communication networks operating in unreliable physical transmission, random access protocol with the collision resolution (CR) scheme is more attractive than the ALOHA family including carrier sense multiple access (CSMA) [IEEE Networks (September 1994) 50–64], due to likely failure on the channel sensing. Being a member of CR family schemes, a protocol known as non-preemptive priority multiple access (NPMA) is utilized in a new high-speed wireless local area network, HIPERLAN, standardized by European Telecommunication Standard Institute (ETSI). A conceptually three-layer CR multiple access protocol generalized from NPMA, supporting single type of traffic, is thus presented and analyzed in this paper. The CR capability of such a protocol (and hence NPMA) is proved to be significant by numerical substantiation that additional collision detection schemes are dispensable; also its throughput/delay performance is excellent when the proportion of the transmission phase to a channel access cycle is large enough (i.e., the winner of contention should transmit all of its packets successively). On the other hand, the simulated performance of NPMA serving integrated traffic is not fully satisfactory, primarily due to its distributed control mode and distinguishing traffic types only by the prioritization process.