Performance evaluation of a receiver-based handshake protocol forCDMA networks

A receiver-based handshake (RBHS) protocol for multipacket channels, such as code-division multiple-access (CDMA) networks, is proposed and its throughput and delay performance is analyzed. This scheme is based on a sensing period and a handshake procedure which can avoid collision and eliminates unwanted transmissions. Several system models under different assumptions, such as completely orthogonal codes and very large processing gain (we call it perfect channel) or with quasiorthogonal codes (nonperfect channel), are investigated. We assume the channel error probability due to other users' interference to be a function of the number of transmissions in a given slot as well as other system parameters. Under a slotted structure with uniform traffic assumption, the system is modeled as a discrete-time two-dimensional Markov chain. The analysis, based on various channel conditions, demonstrates that the average throughput and delay are significantly improved over other spreading code protocols, especially when the channel is likely to accommodate more channel errors, and when the handshaking time is reasonably short compared to the average packet length     

Staggered multicast protocol with collision-free acknowledgement in multihop spread spectrum packet radio networks

The staggered multicast protocol for multihop spread spectrum packet radio networks is suitable for unicasting and broadcasting as well as multicasting. The common-header/transmitter-based spreading code is used for data packet transmission and the receiver-based code is used for acknowledgement packet transmission. By staggering packet transmission the protocol can significantly reduce broadcasting delay. A special addressing method and packet format are also designed to achieve collision-free acknowledgement and multicast capability. Simulation results show that the protocol provides better throughput-delay performance than the common-header/transmitter-based slotted ALOHA protocol.     

Performance of slotted asynchronous CDMA using controlled time ofarrival

A slotted asynchronous (SA) code-division multiple-access communication scheme controlling the time of arrival is proposed for distributed spread-spectrum packet radio networks where the transmission range is limited as in an indoor wireless system. In this scheme, each terminal can send its packet randomly at any one of N_w, possible time instants, equally spaced over one period of direct-sequence spread-spectrum signals. Such transmissions initiated at different time instants can be resolved because of the high time resolution of wide-band signals if the channel delays associated with multipath are small due to limited transmission range. Quasi-synchronous distributed networks are considered to allow timing drift among terminals and also reflect wireless multiple-access channels, in which common-transmitter-based (C-T) and receiver-transmitter-based (R-T) spreading code assignments are adopted to permit a contention mode only for the header portion. The throughput is evaluated under the spread ALOHA assumption on collision events and also by reflecting the effect of the MAI in the header detection process. Theoretical results show that the combination of the SA scheme with C-T assignment results in more significant improvement than the case of R-T assignment, and also the former provides the benefit of the efficient usage of spreading codes in a code-limited environment     

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.     

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     

基于合作分集的新型自动重传协议

研究了一种基于合作分集的新型链路层自动重传协议——合作ARQ协议,传输错误的数据包将由一个中继节点进行重传。根据接收端处理重传数据包的不同方式,探讨了2种协议:1)合作简单ARQ协议,目的节点在收到重传的数据包之后丢弃原始的数据包;2)合作混合ARQ协议,目的节点将重传的数据包和原始数据包进行分集合并。分析了独立慢衰落信道下合作ARQ协议性能,仿真成果证明,合作ARQ协议相比传统ARQ协议能够降低链路层的丢包率,提高了系统的传输性能。     

Code assignment for hidden terminal interference avoidance inmultihop packet radio networks

Hidden terminal interference is caused by the (quasi-) simultaneous transmission of two stations that cannot hear each other, but are both received by the same destination station. This interference lowers the system throughput and increases the average packet delay. Some random access protocols that reduce this interference have been proposed, e.g., BTMA protocol. However, the hidden terminal interference can be totally avoided only by means of code division multiple access (CDMA) schemes. In the paper, the authors investigate the problem of assigning orthogonal codes to stations so as to eliminate the hidden terminal interference. Since the codes share the fixed channel capacity allocated to the network in the design stage, their number must not exceed a given bound. The authors seek assignments that minimize the number of codes used. They show that this problem is NP-complete, and thus computationally intractable, even for very restricted but very realistic network topologies. Then, they present optimal algorithms for further restricted topologies, as well as fast suboptimal centralized and distributed heuristic algorithms. The results of extensive simulation set up to derive the average performance of the proposed heuristics on realistic network topologies are presented     

Performance evaluation of optical code division multiple access systems

In this paper, a new mechanism of faster routing known as message priority and fast routing (MPFR) mechanism in optical code division multiple access (OCDMA) is proposed for optimization of routing performance and to provide effective data transfer. In this proposed work, we have reduced the size of the header bits which are used in MPFR mechanism. In proposed algorithm, with accordance to packet header, the message size is being increased and priority bit is being added which leads to faster data transfer rate and effective data transfer in OCDMA. The transmitter sent the 2D codes to the MPFR which is then added priority bit. If the cover bit in any codes is enabling then the code is considered to be a priority packet and its superior bit then the code is considered to be routing. A modern novel approach which reduces the overhead for fast data transfer is proposed on name of MPFR. Thus the routing can be faster and the codes to be sent are being priorities and send. Thus the OCDMA can now become much faster to be used in critical areas. MPFR protocol, which prioritizes the code with high priority and also it reduces the header processing time of the codes with increase in message size. The prioritization of the code helped to process the particular code first and then rest of the codes and with increase in message size, help to reduce the transmission and processing time of the packet header.     

Nested cooperative encoding protocol for wireless networks with high energy efficiency

Recently, distributed space-time code designs with high cooperative diversity for wireless communication networks, such as ad hoc and sensor networks, have received much attention. Amplify forward and decoding forward are widely used protocols for the cooperative diversity in the wireless communication networks. In both protocols, the information received by relay terminals are "forwarded" to destination or next relay terminals. Since the signals transmitted by relay terminals and those transmitted from the source terminal are correlated, there is information redundancy. To improve the energy efficiency of cooperative networks, we propose an encoding protocol, which is referred to as a nested cooperative encoding protocol. In our proposed protocol, the received signal at each relay terminal is divided into several sub-signals with the nest lattice structure of source information. Each of the sub-signals contains only a partial information with a smaller size of constellation compared to the original information sent by the source terminal. Do a new encoding or modulation by using these sub-signals before transmitting at relay terminals. It is shown that the proposed new protocols can achieve both high cooperative diversity and high energy efficiency.     

一种动态利用码资源的CDMA系统性能研究

本文提出了一种基于随机预约ALOHA访问方式,能支持话音和数据业务的动态使用码资源的码分多址访问协议。在该协议中,话音终端采用预约请求排队访问方式。数据终端采用时隙ALOHA方式传输数据分组。理论分析和计算机仿真结果表明,该协议能有效地提高系统码资源的利用率。在系统处于重负载情况下该协议能优先保证话音业务服务质量,而处于轻负载下系统码资源能为数据业务充分使用。     

Distributed space-time-coded protocols for exploiting cooperative diversity in wireless networks

We develop and analyze space-time coded cooperative diversity protocols for combating multipath fading across multiple protocol layers in a wireless network. The protocols exploit spatial diversity available among a collection of distributed terminals that relay messages for one another in such a manner that the destination terminal can average the fading, even though it is unknown a priori which terminals will be involved. In particular, a source initiates transmission to its destination, and many relays potentially receive the transmission. Those terminals that can fully decode the transmission utilize a space-time code to cooperatively relay to the destination. We demonstrate that these protocols achieve full spatial diversity in the number of cooperating terminals, not just the number of decoding relays, and can be used effectively for higher spectral efficiencies than repetition-based schemes. We discuss issues related to space-time code design for these protocols, emphasizing codes that readily allow for appealing distributed versions.     

Hierarchy schedule sensing protocol for CDMA wireless networks performance study under multipath, multiuser interference, and collision-capture effect

This paper studies a multiple access control protocol, hierarchy schedule sensing protocol, for CDMA wireless data centric networks characterized by high terminal density in a small area. In particular, this paper focuses on the impact of packet collision with capture effect on performance of a network based on the protocol, where a common-coded permission frame beacon is used to schedule-transmission requests to avoid collisions. To further reduce scheduling delay, hierarchical group-based coding is introduced to the scheme. The performance of such a network is analyzed considering packet collisions, capture effect, multipath-interference (Ml), and multiuser interference (MUI) with the help of a Markovian chain model. The average packet collision-rate with and without capture effect is explicitly derived, the performance of the protocol is compared with traditional receiver-based code protocol to show that, despite its low complexity, it is a fairly robust multiple access control protocol featured by uniformly high throughput and low delay.     

Performance analysis of spread spectrum packet radio network withchannel load sensing

A continuous-time Markov-chain model for an asynchronous communication spread-spectrum code-division-multiple-access (CDMA) packet radio network is developed. The network is composed of mutually independent users. The receiver-based code is considered; a terminal with a packet to send looks up the destination's code and transmits on that code. Each user senses the channel load and refrains from transmission if the channel load exceeds the channel threshold. The model makes it possible to study the threshold effect of channel load on the performance of the CDMA packet radio network. Improvements in performance of spread-spectrum packet radio networks due to channel-load sensing are shown. Steady-state results for throughput are obtained     

Group Based Common-Receiver/DS CDMA Wireless Networks And (GBCR) Code Protocol for Its Performance Study

A spreading code protocol (GBCR protocol)suitable for DS CDMA wireless data networks is proposedin this paper. The network is co-ordinated by a centralstation (CS) which maintains a database tracking each user's status. Users are divided intogroups, each of which is assigned a group-basedcommon (GBC) code used by a transmitter in thegroup to acquire the current state of its target. Data communication is allowed only after apositive ACK packet from the CS is received by thetransmitter, so that all successful terminals aresheltered by the CS from possible third-partyinterference which may use the same receiver-based code.Analytical results reveal that the GBCR protocol caneffectively improve network stability andthroughput-delay performance.     

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     

Systematic proximity-detecting codes

This paper defines t-proximity-detecting (t-PD) codes that can detect when a received word is within distance t from the transmitted codeword, when using a four-phase asynchronous communication protocol (or other similar protocols). Proximity-detecting codes can be used to improve the performance of asynchronous buses. A nontrivial t-proximity-detecting code must be unordered. However, not all unordered codes are t-proximity-detecting. This paper characterizes t-PD codes, and presents some properties of such codes. Designs of systematic 1-PD codes, and their generalization to t-PD codes are presented, along with a bound on the number of checkbits     

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.     

Distributed Joint Source-Channel Coding of Video Using Raptor Codes

Extending recent works on distributed source coding, this paper considers distributed source-channel coding and targets at the important application of scalable video transmission over wireless networks. The idea is to use a single channel code for both video compression (via Slepian-Wolf coding) and packet loss protection. First, we provide a theoretical code design framework for distributed joint source-channel coding over erasure channels and then apply it to the targeted video application. The resulting video coder is based on a cross-layer design where video compression and protection are performed jointly. We choose Raptor codes - the best approximation to a digital fountain - and address in detail both encoder and decoder designs. Using the received packets together with a correlated video available at the decoder as side information, we devise a new iterative soft-decision decoder for joint Raptor decoding. Simulation results show that, compared to one separate design using Slepian-Wolf compression plus erasure protection and another based on FGS coding plus erasure protection, the proposed joint design provides better video quality at the same number of transmitted packets. Our work represents the first in capitalizing the latest in distributed source coding and near-capacity channel coding for robust video transmission over erasure channels.     

基于SOA-XPM的光数据包信息头提取

提出一种新型光数据包结构,给出基于该结构的光数据包的组包和信息头提取方案.设计了基于SOA-XPM的全光逻辑与门,利用该与门在2.5Gbit/s的传输速率下对光数据包信息头提取方案进行了数值模拟.结果表明,采用该结构的光数据包具有信息头内容提取容易的优点,适合在全光交换网络中传输.     

New collision-channel model for packet-switched CDMA networks

Packet conflicts in a distributed CDMA network vary with different code protocols which determine packet structure. Improperly designed packet structure is responsible for unrecoverable packet collisions in the channel, resulting in an unacceptably small throughput and large delay. A novel collision-channel model is presented to analyse the network performance concerning the packet contention nature for different CDMA code protocols.<>