Bit-error probabilities of multicode direct-sequencespread-spectrum multiple-access systems

Many techniques for calculating bit-error probabilities (BEPs) of direct-sequence spread-spectrum multiple-access systems (DS-SSMA) have been reported. Among them are the following three techniques: (1) the standard Gaussian approximation; (2) the improved Gaussian approximation; (3) and the simplified improved Gaussian approximation. We extend these techniques to derive the BEPs of multicode DS-SSMA systems. We assess the three techniques by comparing their results with the result of computer simulation     

Computationally efficient bounds for the performance ofdirect-sequence spread-spectrum multiple-access communications systemsin jamming environments

An approach for calculating upper and lower bounds for the probability of error for asynchronous multiple-access spread-spectrum communication systems using deterministic codes is presented. The techniques is then generalized to include multiple-tone jamming. The approach utilizes the cumulative distribution function of individual interference terms. The computational complexity of the technique is calculated to the polynomial-like. Results showing the multiple-access performance of gold codes of lengths 31 and 127 in the presence of jamming are shown. The fact that this computational technique gives upper and lower bounds is rigorously proved using the Riemann-Stieltjes integral     

An efficient self-oscillating mixer for communications

The optical control of the distributed electronics in phased array antennas requires specialized circuits which are compatible with the T/R level data mixing architecture. This paper presents a novel circuit, a push-pull self-oscillating mixer, that can provide the following important advantages: 1) very stable free running oscillation and low FM noise without using a frequency stabilizing dielectric resonator; 2) large subharmonic injection locking range; 3) high frequency conversion efficiency; and 4) low noise figure for the self-oscillating mixer. This proposed circuit efficiently oscillates and mixes with a low prime power consumption. A circuit topology based on this concept was analyzed and designed at 12 GHz using a MESFET pair. Efficient subharmonic injection locking was demonstrated by selecting the optimum operating point corresponding to efficient mixing. The measured down-conversion gain was as high as 13 dB with a double sideband noise figure of 8 dB. This topology can be directly applied for MMIC applications     

Multichannel reservation protocol for packet multiple-access communications

An efficient protocol well suited for the transmission of variable length messages over a group of parallel channels is described. The protocol is applicable to star networks with inbound multiple-access and outbound broadcast channels. Throughput capacity of the inbound channels is analysed and optimised with respect to message length and packet overhead.<>     

An efficient demand-assignment multiple-access scheme for satellitemobile radio dispatch networks

Conventional DAMA (demand-assignment multiple access) designs process mobile radio calls in much the same way as mobile telephone calls. In mobile radio dispatch networks, where the dispatcher is often the resource bottleneck, these designs result in the inefficient use of satellite channels. A novel DAMA design is presented that ameliorates this problem by using the block-calls-queued service discipline, batched processing of several calls by the network dispatcher, and pipelined messaging for channel setup verification. Analysis shows that the proposed design offers advantages in satellite channel utilization and DAMA signaling overhead compared to previous designs. As space segment resources are expected to be very expensive in the mobile satellite systems networks under development, the proposed procedures could result in significant cost savings     

Serial MSK spread-spectrum multiple-access communications

A serial minimum-shift-keyed (MSK) direct-sequence spread-spectrum multiple-access (DS/SSMA) communication system is described and analyzed to obtain the signal-to-noise ratio. The single-channel system generates the same transmitted signals as a corresponding parallel MSK/DS/SSMA system. Hence, the transmitted signals have a constant envelope and desirable spectral properties. However, hardware is required for only one channel, and the multiple-access capability of the system compares favorably with a standard binary DS/SSMA system     

An efficient authentication protocol for mobile communications

In this paper, a new Global System of Mobile Communications (GSM) authentication protocol is proposed to improve some drawbacks of the current GSM authentication protocol for roaming users including: (a) communication overhead between VLR; (b) huge bandwidth consumption between VLR and HLR; (c) storage space overhead in VLR; (d) overloaded in HLR with authentication of mobile stations; and (e) not supporting bilateral authentication. The main contribution of this paper is that it does not only improve the drawbacks listed above but also fits the needs of roaming users. In addition, the proposed protocol does not change the existing architecture of GSM, and the robustness of the proposed protocol is the same as that of the original GSM, which is based on security algorithms A3, A5, and A8.     

Performance of binary and quaternary direct-sequencespread-spectrum multiple-access systems with random signature sequences

The performance of synchronous and asynchronous, binary and quaternary (with and without offset) direct-sequence spread-spectrum multiple-access (DS/SSMA) communication systems using random signature sequences and arbitrary chip waveforms is investigated. The average probability of error at the output of the correlation receiver is evaluated using a characteristic-function approach for these systems. Numerical results are presented that illustrate performance comparisons between systems using random and deterministic signature sequences, synchronous and asynchronous systems, systems with rectangular or sinewave chip waveforms, and binary and quaternary systems with the same data rates and bandwidth. In all cases, the accuracy of the Gaussian approximation is also examined     

Interference suppression to aid acquisition in direct-sequencespread-spectrum communications

The acquisition and tracking systems of a spread-spectrum receiver are probably the most critical components of the receiver, since if they fail to function properly, it is doubtful that the desired signal can be successfully detected. This means that the affect of interference (such as jamming) on the receiver while it is attempting to learn the correct phase position of the incoming code might be especially harmful, since the interference might not allow the receiver to acquire the signal. To address this problem, a narrow-band interference suppression filter is used to enhance the performance of a serial search acquisition scheme for a direct-sequence spread-spectrum receiver. Analytical expressions for the probabilities of error in both the search and lock modes are derived, and numerical results are used to illustrate the sensitivity of the receiver to various system parameters. It is shown that the presence of the rejection filter can be significantly improves the performance of the acquisition system     

Practical capacity calculation for time-hopping ultra-wide band multiple-access communications

In this letter the practical capacity, known as the cutoff rate, of time-hopping (TH) ultra-wide band (UWB) communication system is evaluated for multiple-access channels. The cutoff rate can be used for determining various system tradeoffs. For instance, it is shown in this letter that if synchronization problems would preclude high spreading factors, a suitable number of hops can be used instead to achieve the same performance. Moreover, it is demonstrated that the cutoff rate evaluated here can be a fast way of gaining insights into the multiuser capacity of TH-PPM UWB systems.     

Frequency-hopped multiple-access communications with noncoherent M-ary OFDM-ASK

A noncoherent, bandwidth-efficient modulation scheme is proposed for frequency-hopping multiple-access (FH-MA) networks. The proposed scheme is a combination of noncoherent M-ary amplitude-shift keying (NMASK) and orthogonal frequency-division multiplexing (OFDM). Using this scheme minimizes the required data bandwidth. The number of frequency slots available to the users increases significantly for a fixed spread-spectrum bandwidth (BW/sub SS/). The effect of the multiple-access interference is reduced. Simple and accurate bit error rate expressions have been derived for FH-OFDM-MASK in additive white Gaussian noise channels and for FH-OFDM-ASK in Rayleigh fading channels.     

On the multiple-access capacity of multitone-CDMA communications

This paper derives a bit-error-probability expression for an asynchronous multitone-code-division multiple access (CDMA) system and shows that the multiple-access (MA) capacity of this system is identical to that of a conventional (single-carrier) direct-sequence spread-spectrum system under conditions of equal bandwidth and equal bit rate. It is also shown that using more subcarriers to increase the processing gain does not increase the MA capacity     

脉冲超宽带TH-PPM多址通信的误比特率计算方法

简单地给出了脉冲超宽带(IR-UWB)TH-PPM多址通信方式在信道加性白高斯噪声(AWGN)与多址用户干扰高斯近似条件下的误比特率推导过程。从接收端相关检测时多址用户信号与本地模板信号相互作用产生误相关输出的平均出发,假定多址用户干扰是零均值的高斯过程,分析计算多用户干扰的方差,通过数值计算与系统仿真比较了所得到的结果。     

An efficient method for evaluating network-reliability withvariable link-capacities

An efficient method is proposed to evaluate the network reliability with variable link capacities when the simple paths of the network are known. Most of the evaluation techniques proposed in the literature so far are based on enumerating the k-composite paths, each of which is a union of k simple paths. Although some of those methods lead to correct results, the redundancy is still quite large and may occur repeatedly each time the higher order composite paths are generated. This paper proposes a new method based on the concepts of additivity and eligibility properties defined in the text. The authors identify a composite path as a subnetwork which in general contains more simple paths than those involved in composition, and add only a minimal set of links at each step which gives maximal increase on the maximum capacity flow of the subnetwork. Thereby, they reduce the possible occurrence of redundancy significantly. The number of composite paths considered for the capacity computation is also greatly reduced. Furthermore, it is not necessary to keep the information on how many and which simple paths have been used in each composite path. Some numerical examples illustrate the efficiency of the method     

Selection of spreading sequences for direct-sequencespread-spectrum communications over a doubly selective fading channel

Error probabilities are evaluated for direct-sequence spread-spectrum communications over channels with doubly selective fading. The error probability for such a system depends on the spreading sequence, the autocorrelation function of the fading process, and the receiver signal-to-noise ratio. The focus of this paper is on the effect of the spreading sequence on the performance of differentially coherent detection of binary direct-sequence spread-spectrum signals using a correlator receiver. It is shown that significant performance differences result from different choices of spreading sequence. It is also shown that, given a moderate range of delay and Doppler spreads, sequences can be found which yield low bit error probabilities over the entire range. These are found to be robust with respect to a variety of shapes for the channel autocorrelation function and the full range of signal-to-noise ratios     

FH-MFSK multiple-access communications systems performance in thefactory environment

A frequency-hopped (FH), M-ary frequency-shift-keyed (MFSK), spread-spectrum (SS) communication system operating over the factory radio channel is described. The performance of the system for Rayleigh, Rician, and log-normal multipath fading for factory environments is investigated. The statistics of these channels, based on recent channel modeling studies, are used to evaluate the performance of the FH-MFSK system. A quadrature rule is employed to calculate the channel error probabilities. The average bit error rate (BER) is formulated and is evaluated approximately using Stirling's formula. The numbers of simultaneous users in terms of the number of hopped frequencies, number of MFSK chips, receiver threshold, signal-to-noise ratio, and channel statistics at a fixed BER for Rayleigh, Rician, and lognormal fading channels are determined     

Survey of USSR contributions to random multiple-access communications

A survey is presented of most of the principal results on random multiple-access (RMA) theory obtained in the USSR up to the end of 1983. Relevant background material is provided on the various RMA algorithms discussed.     

An efficient space-frequency coded OFDM system for broadband wireless communications

We propose an efficient space-frequency coded orthogonal frequency-division multiplexing (OFDM) system for high-speed transmission over wireless links. The analytical expression for the pairwise probability of the proposed space-frequency coded OFDM system is derived in slow, space- and frequency-selective fading channels. The design criteria of trellis codes used in the proposed system are then developed and discussed. It is shown that the proposed space-frequency coded OFDM can efficiently achieve the full diversity provided by the fading channel with low trellis complexity, while for traditional space-frequency coded OFDM systems, we need to design space-time trellis codes with high trellis complexity to exploit the maximum achievable diversity order. The capacity properties of space-frequency coded OFDM over multipath fading channels are also studied. Numerical results are provided to demonstrate the significant performance improvement obtained by the proposed space-frequency coded OFDM scheme, as well as the excellent outage capacity properties.     

An efficient optimisation scheme for scalable surveillance centric video communications

State-of-the-art coders have been optimised over years according to the needs of the broadcasting industry. There are however key applications of coding technology whose challenges and requirements substantially differ from broadcasting. One of these key applications is surveillance. In this paper an efficient approach for surveillance centric joint source and channel coding is proposed. Contrasting conventional coders, the proposed system has been developed according to the requirements of surveillance application scenarios. It aims at achieving bit-rate optimisation and adaptation of surveillance videos for storing and transmission purposes. In the proposed approach the encoder communicates with a video content analysis (VCA) module that detects events of interests in video captured by CCTV. Bit-rate optimisation and adaptation is achieved by exploiting the scalability properties of the employed codec. Temporal segments containing events relevant to surveillance application are encoded using high spatio-temporal resolution and quality while the portions irrelevant from the surveillance standpoint are encoded at low spatio-temporal resolution and/or quality. Furthermore, the approach jointly optimises the bit allocation between the wavelet-based scalable video coder and forward error correction codes. The forward error correction code is based on the product code constituting of LDPC codes and turbo codes. Turbo codes show good performance at high error rates region but LDPC outperforms turbo codes at low error rates. Therefore, the concatenation of LDPC and TC enhances the performance at both low and high signal-to-noise (SNR) ratios. The proposed approach minimises the distortion of reconstructed video, subject to constraint on the overall transmission bit-rate budget. Experimental results clearly demonstrate the efficiency and suitability of the proposed approach in surveillance applications.