Capacity of synchronous coded DS SFH and FFH spread-spectrummultiple-access for wireless local communications

The performance of synchronous spread-spectrum multiple-access (SSMA) communications based on direct-sequence (DS), slow frequency-hopped (SFH), and fast frequency-hopped (FFH) systems for wireless local communications of micro-cellular personal communications is analyzed. Using an indoor multipath fading channel model with clusters of arriving rays, we investigate multiuser DS systems with RAKE and diversity reception by selection combining (SC), multiuser SFH systems with equal-gain (EG) diversity reception, and multiuser FFH systems with correlated EG and self-normalization (SN) combining techniques. Reed-Solomon codes are considered to further improve the system performance. Given a fixed available bandwidth with narrow band interference (NBI), capacities and packet error rates are determined under various system configurations. Total capacities of hybrid frequency-division multiple-access (FDMA)/SSMA (DS and SFH) systems are compared with those of wide-band SSMA systems. For high data rate communications, wide-band DS-SSMA systems have larger capacities than hybrid FDMA/DS-SSMA systems. For low data rate communications, a capacity comparison between wide-band DS-SSMA and hybrid FDMA/DS-SSMA systems depends on fading statistics. Hybrid FDMA/SFH-SSMA systems have larger capacities than wide-band DS-SSMA systems, FFH-SSMA systems could not provide satisfactory performance due to correlation among hopping bands     

Costas序列在多用户雷达系统中的应用研究

讨论了跳频码的构造与性能,着重介绍了Costas序列的结构,用Costas序列设计跳频码能获得理想的自模糊和较好的互模糊性能.建立了跳频扩频信号的数学模型,给出了子脉冲正交的条件.论述了Costas序列的自(互)相关特性,给出了置换序列互相关函数的实用性质及模糊函数的求取算法,并进行了性能仿真,研究了Costas序列互模糊函数的特性,阐述了多用户系统中减小用户间相互干扰的方法.     

One-coincidence sequences with specified distance between adjacentsymbols for frequency-hopping multiple access

Frequency hopping spread-spectrum systems have been popular in multiple-access communication systems. In such frequency-hopping multiple-access systems, multilevel sequences are used to specify which frequency will be used for transmission at any given time. One-coincidence sequences with specified distance between adjacent symbols for frequency-hopping multiple access are described. In such sequences, the distances between any adjacent symbols in any sequence are more than some specified amount. A theoretical bound is derived for the sequences, and two theorems on the construction of the sequences are given     

On the error probability of coded frequency-hopped spread-spectrummultiple-access systems with more than one code symbol per dwellinterval

The multiple-access capability of an asynchronous, frequency-hopped spread-spectrum (FH-SS) communication system employing error correcting codes is reviewed. Many current FH-SS systems employ error correcting codes with more than one code symbol per dwell interval. A method of computing the codeword error probability induced in such spread-spectrum systems is presented. The codeword error probabilities induced in spread-spectrum systems utilizing more than one versus one code symbol per dwell interval are compared. It is concluded that FH-SS systems with one code symbol per dwell interval are more efficient in combating multiple-access interference than FH-SS systems with more than one code symbol per dwell interval     

跳频序列设计理论的研究进展

跳频技术具有抗干扰和多址组网性能，在军事无线电通信、民用移动通信、现代雷达和声纳等电子系统中具有重要的应用。跳频序列用于控制载波频率随机时间的变化规律，其性能对跳频系统的性能有重大影响。本文综述跳频序列设计理论的研究成果，并指出今后的发展方向。     

Coherent Hybrid DS-SFH Spread-Spectrum Multiple-Access Communications

The performance of synchronous and asynchronous hybrid direct-sequence/slow-frequency-hopped spread-spectrum multiple-access communications over additive white Gaussian noise channels is examined. Systems employing binary or quaternary phase-shift-keying modulation with coherent demodulation are investigated. Both deterministic and random signature sequences and frequency-hopping patterns are considered and several possible assignments for them are discussed. It is shown that the multiple-access capability of hybrid spread-spectrum is superior to that of pure frequency-hopped spread-spectrum, and inferior to that of pure direct-sequence spread-spectrum for systems with identical bandwidth expansion which employ the same data modulation and demodulation scheme and random hopping patterns and signature sequences.     

Adaptive spread-spectrum multicarrier multiple-access over wirelines

In this paper, we investigate the dynamic resource allocation adapted to spread-spectrum multicarrier multiple-access (SS-MC-MA) systems in a multiuser power line communication (PLC) context. The developed adaptive system is valid for uplink, downlink, as well as for indoor and outdoor communications. The studied SS-MC-MA system is based on classical multicarrier modulation like digital multitone (DMT), combined with a spread-spectrum (SS) component used to multiplex several information symbols of a given user over the same subcarriers. The multiple-access task is carried out using a frequency-division multiple-access (FDMA) approach so that each user is assigned one or more subcarrier sets. The number of subcarriers in each set is given by the spreading code length as in classical SS-MC-MA systems usually studied in the wireless context. We derive herein a new loading algorithm that dynamically handles the system configuration in order to maximize the data throughput. The algorithm consists in an adaptive subcarrier, code, bit, and energy assignment algorithm. Power-spectral density constraint due to spectral mask specifications is considered, as well as finite-order modulations. In that case, it is shown that SS-MC-MA combined with the proposed loading algorithm achieves higher throughput than DMT in a multiuser PLC context. Because of the finite granularity of the modulations, some residual energy is indeed wasted on each subcarrier of the DMT spectrum. The combining of a spreading component with DMT allows to merge these amounts of energy so that one or more additional bits can be transmitted in each subcarrier subset leading to significant throughput gain. Simulations have been run over measured PLC channel responses and highlight that the proposed system is all the more interesting than the signal-to-noise ratio is low.     

Chaotic-laser-based true random sequence generation for spread-spectrum communications

We propose a scheme for spread-spectrum communications using true random sequences generated by chaotic semiconductor lasers as spreading codes.These sequences can eliminate the inherent periodicity of pseudorandom sequences,enlarge the capacity of spread-spectrum codes,improve communication security,and increase the number of users of the system.When a true random sequence with an appropriate length is used as the spread-spectrum code and the information speed is maintained constant,the system acquires a greater spreadspectrum gain and a lower bit-error ratio(BER) than the traditional spread-spectrum system.The communication security is also enhanced.The BER smoothly increases with the number of users,which indicates the good multipleaccess capability of the system.     

Bit-Interleaving in Fast FH/SSMA Systems with M-FSK Modulation

The effects of bit-interleaving on the performance of convolutional codes and turbo codes in fast frequency- hop/spread-spectrum multiple-access systems with M-FSK modulation are investigated. It is observed that bit-interleaving induces two counter-acting forces on decoder performance. On the one hand, bit-interleaving disperses consecutive error bits caused by a noisy M-ary signal and makes the errors more correctable. On the other hand, the same measure makes it difficult for the decoder to make use of the bit dependency information. Both theoretical upper bounds and simulation results show that bit- interleaving degrades the performance of soft-decision decoded convolutional codes and turbo codes.     

Probability of error in frequency-hop spread-spectrummultiple-access communication systems with noncoherent reception

Expressions are developed for the probability of error for asynchronous frequency-hop spread-spectrum multiple-access networks using Markov hopping patterns and binary frequency shift keying (BFSK) with one symbol transmitted per hop. The expressions are exact when there is one interfering user and orthogonal BFSK is used. They provide excellent approximations when there are more than one interfering user. It is also shown that the error probability when Markov hopping patterns are used is a good approximation to the error probability when memoryless hopping patterns are used. By computing the channel capacity and the associated throughput, a simple hard decision receiver is shown to perform much better than a receiver using perfect side-information to erase the symbols transmitted on hops that were hit when all the users have the same power and one binary symbol is transmitted per hop     

Conditions for synchronisation and corresponding user capacities for spread-spectrum multiple-access systems

User capacities for direct-sequence spread-spectrum multiple-access communication systems are obtained, for the situation where a receiver has to synchronise to its wanted signal in the presence of other users' transmissions, under all relative phase conditions. The use of both conventional and rapid-acquisition codes is considered.     

Golomb Costas序列的结构及其在OFDM系统中的应用

研究了用循环移位法获得的Golomb Costas序列族的特性,建立了含有一个间隙行和一个间隙列的Golomb Costas序列的结构理论,深入研究了含有一个间隙行和一个间隙列的Golomb Costas序列的代数结构、构造方法和自（互）相关特性,并证明了相关的定理。探索了用含有一个间隙行和一个间隙列的Golomb Costas序列设计OFDM 系统中跳频图样的方法,举例说明了如何设计跳频码和怎样将跳频码分配给 OFDM 系统中的用户。用含有一个间隙行和一个间隙列的Golomb Costas序列设计跳频码能获得理想的自相关特性,并且当无线通信系统中多普勒频移受限时能获得极佳的互相关性能。     

Soft multiuser demodulation and iterative decoding for FH/SSMA with a block turbo code

The number of users that can be supported by frequency-hopped, spread-spectrum multiple-access systems can be increased greatly by using multiuser demodulation and iterative decoding. In the receiver employed hard-decision multiuser demodulation followed by iterative decoding, users exchange decoded information with each other. Additional information from multiuser demodulation in the first decoding iteration is limited by the hard-decision output of the multiuser demodulator. The error-correction used was an errors-and-erasures Reed-Solomon (RS) decoder. We revisit hard-decision demodulation and conventional RS decoding. Hard-decision multiuser demodulation is modified to provide a soft output, which is then given to a nonbinary block turbo code with shortened RS codes as the constituent codes. An iterative multiuser decoding algorithm is developed to do soft multiuser interference cancellation. This soft receiver with soft demodulation and decoding is shown to be more resistant to multiuser interference and channel noise, especially at lower values of signal-to-noise ratio. The results show a great improvement in the ability of the system to support more users (more than three times in some cases), as compared with systems that erase all hits or employ hard-decision multiuser demodulation followed by RS code. We examine the proposed method for synchronous as well as asynchronous frequency-hopped systems in both AWGN and fading channels.     

A new family of optical code sequences for use in spread-spectrumfiber-optic local area networks

The problem of the algebraic construction of a particular family of optical codes for use in code-division multiple-access (CDMA) fiber-optic local area networks (LANs) is treated. The conditions that the code families have to satisfy when used in such systems are reviewed. The new codes are called quadratic congruence codes, and the construction of the corresponding sequences is based on the number-theoretic concept of quadratic congruences. It is shown that p-1 codes exist for every odd prime p and can serve as many as p-1 different users in the CDMA fiber-optic system. The codes belong to the family of optical orthogonal codes, their auto- and cross-correlation properties are established, and their performance is compared to that of the previous optical codes. Examples of the codes and examples of their auto- and cross-correlation functions are given     

跳频码设计新方法

本文首次将有限域中的置换多项式引入跳频码的设计之中,并给出了若干类自相关和互相关特性都很好的全频道跳频码。例如文中第2类码是目前已知的各方面综合性能最好的全频道跳频码。     

Optimal large linear complexity frequency hopping patterns derivedfrom polynomial residue class rings

We construct new sequences over finite rings having optimal Hamming correlation properties. These sequences are useful in frequency hopping multiple-access (FHMA) spread-spectrum communication systems. Our constructions can be classified into linear and nonlinear categories, both giving optimal Hamming correlations according to Lempel-Greenberger (1974) bound. The nonlinear sequences have large linear complexity and can be seen as a generalized version of GMW sequences over fields     

A novel frequency-hopping spread-spectrum multiple-access network using M-ary orthogonal Walsh sequence keying

A novel frequency-hop spread-spectrum multiple-access network employing M-ary orthogonal Walsh sequence keying with noncoherent demodulation is proposed. The transmitted Walsh sequence is overlaid by a user-specific pseudonoise sequence to reduce the effect of multiple-access hits. Two Gaussian approximations for the multiple-access interference from both the dehopped slot and its neighboring slots are developed and are used to analyze the performance of the proposed network for synchronous and asynchronous hopping under nonfading and Rayleigh fading channels. The effect of imperfect hop timing synchronization at the receiver is also analyzed. It is shown that the proposed network offers significantly improved network throughput compared to networks based on traditional M-ary frequency-shift keying modulation.     

Performance of chip coding in FFH SSMA systems

This paper proposes chip coding using convolutional codes for fast frequency-hopping spread-spectrum multiple-access (FFH-SSMA) systems. Its performance is evaluated and compared with that of repetition coding which is most commonly used in FFH systems. In our proposal, an information symbol is encoded by a convolutional code of rate 1/n and n chips are transmitted through a frequency hopper. We consider three models when perfect side information (PSI) is available, no side information (NSI) is available, and the ratio threshold test (RTT) is used. The probability density functions (PDFs) of the received signal are derived for asynchronous hopping systems. The performances of convolutional coding with threshold decoding and Viterbi decoding are presented under the constraint of fixed total bandwidth and information bit rate. In comparison with repetition codes, it is found that convolutional codes drastically enhance the system performance. It is identified that Viterbi decoding with RTT offers the most significant performance improvement     

Coherent frequency hopping multiple access (CFHMA) with multiuserdetection for mobile communication systems

This paper proposes a new multiple-access (MA) scheme, coherent frequency hopping MA (CFHMA) with multiuser detection, which effectively obtains the diversity effect for realizing spectrally efficient mobile communications, CFHMA is fundamentally equivalent to a coherent fast frequency hopping frequency-division MA (FDMA) that incorporates low spreading factor direct-sequence (DS) code-division MA (CDMA). Multiple users occupy the same frequency band, and they are simultaneously detected by multiuser detection. There are several implementations of CFHMA. Two major techniques are introduced: coherent hybrid DS fast FH (FFH) (CHYB-DS-FFH) and interleaved FH (IFH). This paper focuses on IFH and discusses its principle of operation, transmission system configuration, and performance aspects. The results suggest the feasibility of a spectrally efficient mobile radio system     

A multiuser interference cancellation technique utilizingconvolutional codes and orthogonal multicarrier modulation for wirelessindoor communications

This paper suggests that multicarrier modulation reduces the complexity and the delay caused by the multiuser interference cancellation process utilizing convolutional codes. For spread spectrum multiple access, multiuser interference (interference due to signals from other users) limits the performance of the communication link. To remove this interference, a multiuser interference cancellation technique which utilizes orthogonal convolutional codes has been proposed for the uplink (mobiles to a base station) of the cellular code-division multiple-access (CDMA) systems. However, this technique requires large interleavers and huge memory, or artificial multipath diversity and a RAKE system to achieve sufficient coding gain if it is applied to wireless indoor communications and fading is slow compared to the data rate. To reduce the complexity of the canceller, multicarrier modulation is employed as it provides frequency diversity gain and coding gain without the interleavers or a RAKE system. This paper shows that multicarrier modulation reduces the complexity of the canceller and still provides sufficient coding gain in order to cancel the multiuser interference. A canceller with decoding in the initial decision and multicarrier modulation improves the capacity by a factor of 1.4 as compared with a canceller without decoding