A reservation random-access protocol for voice/data integratedspread-spectrum multiple-access systems

Most code-division multiple-access (CDMA) systems described in the literature provide only one single service (voice or data) and employ the strategy of “one-code-for-one-terminal” for code-assignment. This assignment, though simple, fails to efficiently exploit the limited code resource encountered in practical situations. We present a new protocol called reservation-code multiple-access (RCMA), which allows all terminals to share a group of spreading codes on a contention basis and facilitates introducing voice/data integrated services into spread-spectrum systems. The RCMA protocol can be applied to short-range radio networks, and microcell mobile communications, and can be easily extended to wide area networks if the code-reuse technique is employed. In RCMA, a voice terminal can reserve a spreading code to transmit a multipacket talkspurt while a data terminal has to contend for a code for each packet transmission. The voice terminal will drop a long delayed packet while the data terminal just keeps it in the buffer. Therefore, two performance measures used to assess the proposed protocol are the voice packet dropping probability and the data packet average delay. Theoretical performance is derived by means of equilibrium point analysis (EPA) and is examined by extensive computer simulation     

Random assignment/transmitter-oriented code scheme for centralizedDS/SSMA packet radio networks

We address an issue of channel sharing among users by using a random assignment/transmitter-oriented (RA/T) code scheme which permits the contention mode only in the transmission of a header while avoiding collision during the data packet transmission. Once the header is successfully received, the data packet is ready for reception by switching to one of the programmable matched-filters. But the reception may be blocked due to a limited number of matched-filters so that this effect is taken into account in our analysis. We also consider an acknowledgment scheme to notify whether the header is correctly detected and the data packet can be processed continuously, which aims at reducing the interference caused by unwanted data transmission. For a realistic analysis, we integrate the detection performance at the physical level with the channel activity at the link level through a Markov chain model. It is shown that compared to classical code-division multiple-access (CDMA) systems, a reduction in the receiver complexity of a half is allowed by choosing a proper number of RA/T codes without losing the performance quality in view of the normalized throughput     

一个无线传感器网络中的ipv6协议栈头部压缩方案

提出了一个无线传感器网络中的IPv6协议栈的头部压缩方案,包括IPv6头部、扩展头部和UDP头部的压缩.该方案易于实现,能够较大程度的减少无线传感器网络中报文的传输时间,从而降低能量消耗,延长节点寿命.     

Spreading code protocols for distributed spread-spectrum packetradio networks

Spreading code protocols for a distributed spread-spectrum packet radio network are presented. A distributed single-hop system (i.e. each terminal can hear all other terminals) with the users approximately synchronized and a set of prespecified spreading codes are presented. The spreading code protocol is a policy for choosing a spreading code to be used, given that a terminal has a packet to send, and a policy for monitoring spreading codes, given that a terminal is idle. A slotted system where a packet occupies a number of slots is considered, and two protocols that involve changing the spreading code of a transmission after an initial header is transmitted are presented. In one protocol, the header is transmitted on a common code, and in the other it is transmitted on a receiver-based code, the rest of the packet being transmitted on a transmitter-based code. In the receiving mode, a terminal monitors either a common code, in the first case, or a receiver-based code in the latter. Upon recognizing its own address and the source address, the receiver dynamically switches to a despreading code corresponding to the source. Throughput results are obtained for the case of geometrically distributed packet lengths     

On the performance of centralized DS-SS packet radio networks withrandom spreading code assignment

The paper presents a random spreading code assignment scheme for enhancing channel efficiency in centralized DS-SS packet radio networks which employ a multiple-capture receiver for each code channel. Compared to the common code case, this approach requires a modest increase in receiver complexity, but the number of distinct spreading codes being used is considerably less than the number of radios in the network. A general theoretical framework for evaluation of collision-free packet performance in each code channel is described, in which the possibility of collision-free transmission is conservatively estimated using a combinatorial method, and the effects of asynchronous multiple-access interference are characterized in terms of the primary and secondary user interferences. At the link level, the capture and throughput performances are evaluated for a proper set of codes, and compared with the results from the common code scheme. It is shown that the use of a random assignment scheme with more than one code results in a higher performance gain, and most of this gain can be achieved with just two distinct spreading codes     

High-throughput time group access MCR-SS-CSMA/CA for wireless ad hoc networks with layered-tree topology

Multi-hop packet transmission error due to packet collision is a serious issue for realizing large-scale wireless ad hoc networks. In order to solve the issues, a multicode-reception spread-spectrum (MCR-SS)-CSMA/CA scheme is proposed as multiple access scheme for layered-tree networks. This scheme is further improved by adding a time group access (TGA) technique to gain higher interference reduction between nodes. The proposed TGA scheme divides the layered-tree network into upper subnets group and lower subnets group, thus reducing collision probability among subnets. Network throughput and data delivery ratio for the proposed scheme are analyzed by simulations based on the IEEE 802.15.4/ZigBee specification. Simulation results show that the proposed schemes can improve packet delivery ratio and network throughput remarkably.     

A hybrid interleaving scheme that enables packet switching onmultiple-access radio communication channels

An interleaving technique is proposed that is memory, delay, and packet efficient for demand assignment multiple-access, packet-switched transmission with frequency-hopped survivability interleaved signals over jammed or scintillated radio channels. This hybrid interleaving scheme concatenates the convolutional interleaver and the block interleaver     

A novel Qos-aware MAC scheme using optimal retransmission for wireless networks

This paper proposes a novel Medium Access Control scheme for low cost, single-hop wireless networks where the source nodes have a transmitter module but no receiver module and hence they can only transmit data to a sink but cannot receive any control signals, like an ACK or NAK, from any other node. The goal of the proposed scheme is to provide QoS (in terms of packet delivery probability) to the nodes in such a network, where the existing schemes like polling or scheduled transmissions, CSMA and ARQ will be ineffective because of the unavailability of a receiver module at the nodes. The proposed scheme uses distributed control and allows the nodes to transmit each packet an optimal number of times at random instants in time within the packet generation interval. We define two optimization problems based on minimizing total network traffic and maximizing the delivery probability of the class of nodes requiring the highest QoS, respectively, and develop mathematical formulae and efficient algorithms to solve them. Numerical analysis and simulation results show that our scheme can provide high QoS to networks of different sizes.     

A dynamic CDMA network for multicore systems

Code-division multiple-access (CDMA) is a data transmission method based on the spreading code technology, wherein multiple data streams share the same physical medium with no interference. A novel architecture for on-chip communication networks based on this approach is devised. The proposed design allows sharing coding resources among network?s users through the use of dynamic assignment of spreading codes. Data transmission latency is reduced by adopting a parallel structure for the coding/decoding circuitry. A 14-node CDMA network based on the proposed architecture is synthesised using 65 nm ST technology library. Performance analysis reveals that the proposed approach achieves significantly lower data packet latency compared to both conventional CDMA and packet switched network-on-chip implementations. Large area and power savings compared to existing approaches are also obtained.     

Joint Delay-Power Multiple Packet Capture Scheme for Spread-Spectrum Slotted ALOHA Packet Radio Networks

In this paper, a joint delay-power multiple packet capture scheme, that can collect multiple packets simultaneously from different terminals with both delay and power captures, is presented. The corresponding joint delay-power capture probabilities for a spread-spectrum slotted ALOHA packet radio networks where all terminals use a common spreading code under Rayleigh fading with power control are derived. Throughput and delay performance of the spread-spectrum slotted ALOHA packet radio networks with the joint delay-power multiple packet capture effect are shown by our simulation results to be significantly improved compared with the existing schemes.     

QoS based fair resource allocation in multi-cell TD/CDMA communication systems

Abstract-In a wireless multimedia code division multiple access (CDMA) system, the resources in terms of transmission rate and power should be efficiently distributed to each user to guarantee its quality-of-service (QoS) requirements. In, this paper, a resource allocation algorithm which combines packet scheduling and power assignment is proposed to achieve efficient resource utilization under QoS constraints. The packet scheduling is based on the fair packet loss sharing (FPLS) principle, and the power assignment is determined by the received power limited (RPL) scheme. 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 with QoS satisfaction. The RPL scheme minimizes the received power for each packet. Given the propagation path loss, it in turn minimizes the transmitted power as well. The intercell interference from the scheduled packets is also limited in order to increase the system capacity.     

A novel random wireless packet multiple access method using CDMA

Random packet CDMA, a novel packet-based multiple access scheme for connectionless, uncoordinated random channel access is proposed. Random packet CDMA, or RP-CDMA, utilizes a novel packet format which consists of a short header and a data portion. Each header is spread with a unique spreading code which is identical for all users and packets, while the data portion of each packet is spread by a randomly chosen spreading sequence. The receiver operates in two stages: header detection and data detection. For header detection a conventional spread spectrum receiver is sufficient. Headers are spread with a large enough processing gain to allow detection even in severe interference. The data portion is decoded with a sophisticated receiver, such as a multiuser detector, which allows for successful decoding of overlapping active packets. It is shown that the RP-CDMA system is detector capability limited and that it can significantly outperform spread ALOHA systems whose performance is limited by the channel collision mechanism. RP-CDMA also experiences a much smaller packet retransmission rate than conventional or spread ALOHA, and provides better spectral efficiencies.     

Signal recognition and signature code acquisition in CDMA mobilepacket communications

Fast and reliable signal sense and signature code synchronization for direct-sequence spread-spectrum (DS-SS) signals are key issues in the design of the receiver for modern packet code-division multiple-access (CDMA) radio networks for mobile communications; this motivates the study of the signal recognition and code-acquisition (SR/CA) scheme we describe in this paper. Specifically, starting from elementary estimation and detection theory criteria, we work out a noncoherent parallel SR/CA algorithm that is suited to a full-digital implementation in a single application-specific integrated circuit (ASIC). The results of a theoretical analysis of such a scheme, encompassing additive white Gaussian noise (AWGN) and multiple-access interference (MAI), are integrated and validated by an overall time-domain system simulation. We also evaluate through a simplified approach the impact of some degradation factors on the overall circuit performance, namely, sampling epoch and carrier frequency offset and 1-b signal quantization, to allow optimization of the design parameters as a function of the characteristics of the received signal     

Distributed Medium Access Control Next-Generation CDMA Wireless Networks

The next-generation wireless networks are expected to have a simple infrastructure with distributed control. In this article, we consider a generic distributed network model for future wireless multimedia communications with a code-division multiple access (CDMA) air interface. For the medium access control (MAC) of the network model, we provide an overview of recent research efforts on distributed code assignment and interference control and identify their limitations when applied in next-generation wireless networks supporting multimedia traffic. We also propose a novel distributed MAC scheme to address these limitations, where active receivers determine whether a candidate transmitter should transmit its traffic or defer its transmission to a later time. Simulation results are given to demonstrate the effectiveness of the proposed distributed MAC scheme.     

Dynamic random access code assignment for prioritized packet data transmission in WCDMA networks

We propose a measurement-based dynamic random access (RA) code assignment procedure for prioritized packet data transmission in wideband code-division multiple access (WCDMA) networks. This dynamic adaptation process is based on analytical performance results derived for random packet access under Rayleigh fading in WCDMA networks. The performance of the proposed measurement-based RA code assignment procedure with three different adaptation methods is evaluated by using computer simulations. The performance of the proposed scheme is compared with those of a retransmission control-based and static channel allocation-based prioritized packet access scheme. An integrated (physical layer and link layer) delay-throughput performance model is presented for finite population RA WCDMA systems. The proposed dynamic RA code assignment procedure can be used in an adaptive quality of service (QoS) framework for dynamically adjusting the QoS of prioritized RA data traffic in the evolving WCDMA-based differentiated services wireless Internet protocol networks.     

Distributed code assignments for CDMA packet radio networks

Code-division multi-access (CDMA) techniques allow many users to transmit simultaneously in the same band without substantial interference by using approximately orthogonal (low cross-correlation) spread-spectrum waveforms. Two-phase algorithms have been devised to assign and reassign spread-spectrum codes to transmitters, to receivers and to pairs of stations in a large dynamic packet radio network in polynomial times. The purpose of the code assignments is to spatially reuse spreading codes to reduce the possibility of packet collisions and to react dynamically to topological changes. These two-phase algorithms minimize the time complexity in the first phase and minimize the number of control packets needed to be exchanged in the second phase. Therefore, they can start the network operation in a short time, then switch to the second phase with the goal of adapting to topological changes. A pairwise code-assignment scheme is proposed to assign codes to edges. Simulations based on well-controlled topologies (sparse topologies) show that the scheme requires much fewer codes than transmitter-based code assignment, while maintaining similar throughput performance     

卫星IP网络包头压缩技术分析

由于IP数据包头带来的较大开销,在卫星链路上传输IP数据包效率较低。分析了健壮性头标压缩协议(ROHC)在卫星通信系统中应用的可行性,在Linux平台对ROHC进行了实现。描述了ROHC在内核中的实现方法,提出了ROHC在内核中的嵌入方式,介绍了压缩器和解压器的实现流程,对ROHC实现进行了测试和性能分析。实验测试表明,采用ROHC极大减少了IP数据包头长度,大大提高了IP业务卫星带宽利用率。     

Novel Fastest Retransmission and Rate Control Schemes for Improving TCP Performance in Wireless Ad Hoc Networks

A number of different authors have considered the problem of performance degradation of transmission control protocol (TCP) in wireless ad hoc networks. We herein show that pauses in packet transmission due to packet losses are the fundamental cause of performance degradation of TCP in wireless ad hoc networks. To minimize the duration of packet transmission pauses, we propose a fast retransmission scheme for improving TCP performance in consideration of the inter-operability of previously deployed TCPs in wireless ad hoc networks. We also propose an additional rate control scheme for TCPs to reduce the probability of packet contention. Using OPNET and NS2 simulations, we show that our proposed schemes can provide a much better performance than conventional TCPs.     

无线Ad hoc网络中的联合信源信道有效用户安全识别方法

无线Ad hoc网络采用无线信道、有限电源、分布式控制等技术,因此存在信道安全威胁和大量的能量消耗等问题。为了克服以上问题,论文提出了一种基于DS-CDMA的无线Ad hoc联合信源信道有效用户安全识别方法,对已知头标识采用加密保护,在接收机结点处应用基于子空间的多用户检测技术,并通过有效用户识别方法只对头部数据进行有效用户安全识别,。仿真实验表明:本方法改善了漏警概率和活动用户数估计精度,不但减少了丢弃重发,节省无线模组工作时的能量消耗,同时达到了对有效用户安全识别的目的,提高了信道安全性能。     

Performance of space-division multiple-access (SDMA) with scheduling

Efficient exploitation of spatial diversity is fundamentally important to resource critical wireless applications (Tsoulos 1999). In this paper, we first study the performance of intelligent scheduling for space-division multiple-access (SDMA) wireless networks (Suard 1998, Farsakh 1998). Based on the existing scheme, we propose a new medium access protocol (MAC) for multimedia SDMA/time-division multiple-access (TDMA) packet networks (Xu 1994, Ward 1993). The improved protocol performs scheduling based on users' spatial characteristics and quality-of-service parameters to achieve throughput multiplication and packet delay reduction. Performance of SDMA with scheduling is evaluated under mixed audio and data traffic patterns and results show that significant improvement in network performance can be achieved under the new protocol.