Performance of one-hop/symbol FHMA for cellular mobilecommunications

This paper is concerned with the bit-error rate (BER) performance of a cellular one-hop/symbol frequency-hopping multiple-access (FHMA) system operating through a multipath Rayleigh fading channel. M-ary frequency shift keying modulation with noncoherent square-law envelope demodulation and Reed-Solomon (RS) coding is considered. The multiple-access and adjacent cell interference of the cellular FHMA system has been studied. In order to illustrate how sensitive both systems are to the near/far problem, performance of the FHMA system is compared with that of a direct-sequence code-division multiple-access system for an equal system bandwidth. Also, this paper investigates the effect of the values of frequency reuse factor (N) on the system capacity of the cellular frequency-hopping system     

基于分组密码的跳频序列多址接入性能分析

基于3DES迭代型分组密码产生的跳频序列,构造了一种跳频组网的随机多址接入方案模型。在此基础上分析了跳频码分多址的系统接入性能,从理论上推导出跳频图案碰撞引起的误分组率、跳频组网的吞吐量和归一化吞吐率,证明数据分组长度M与可用频隙数q的比值是决定跳频码分多址系统性能的重要因素。计算机仿真结果验证了理论的正确性,同时也证明了基于分组密码的跳频序列具有较好的跳频多址组网性能。     

Analysis of FHMA performance on block cipher based frequency-hopping sequences

Based on the triple Data Encryption Standard (DES) block cipher frequency-hopping (FH) sequences, a kind of packet protocol for frequency-hopping multiple-access (FHMA) network is suggested in this paper. In theory, the performances of both the packet error and the throughput are derived, which shows that the ratio of the packet length M to the frequency slots number q is most key parameter to determine the FHMA system performance under the condition of large user number. Computer simulation results of 3-DES FH sequences compared with those of the chaotic FH sequences are also included to support our developments.     

Residue number system assisted fast frequency-hopped synchronous ultra-wideband spread-spectrum multiple-access: a design alternative to impulse radio

Ultra-wideband (UWB) systems having a bandwidth on the order of gigahertz have received wide attention both in the US and in Europe. The family of UWB systems may communicate either, by generating ultra-wideband signals or with the aid of innovatively combining conventional narrowband, wideband, or broadband signals. At the time of writing, UWB systems have only been implemented using ultra-wideband signals, such as those known from impulse radio systems. Hence, in this paper, UWB systems using narrowband signals are explored as a design alternative, which are based on the well-known family of frequency-hopping (FH) spread-spectrum multiple-access techniques. In the proposed UWB system, FH is implemented using multistage frequency-hopping multiple access (MS/UWB FHMA). We highlight the principles of the synchronous MS/UWB FHMA communication system, investigate the associated spectrum assignment, and the residue number system (RNS) based FH strategy: detection of the received signal can be achieved with the aid of existing fast FH signal detection schemes. Our study shows that the RNS assisted FH strategy is capable of efficiently dividing the huge number of users supported by the synchronous MS/UWB FHMA system into a number of reduced-size user groups, where the multiuser interference only affects the users within the same group. Since the number of users in each group is only a small fraction of the total number of users supported by the synchronous MS/UWB FHMA system, advanced multiuser detection algorithms can be employed for achieving near-single-user performance at an acceptable complexity. Our results show that MS/UWB FHMA is capable of supporting an extremely high number of users, while employing relatively simple receivers.     

Maximum likelihood combining for noncoherent and differentially coherent frequency-hopping multiple-access systems

The frequency-hopping multiple-access (FHMA) approach to digital mobile radio provides diversity gain against frequency selective fading. Optimum combining methods, in the maximum likelihood sense, are derived for FHMA systems with either noncoherent or differentially coherent detection. In the optimum combining structure, the detector outputs are first passed through a nonlinearity and then a linear combiner.     

基于分组密码的跳频序列族构造

基于迭代型分组密码的理论体系,本文从工程实现的角度提出了一种用于跳频码分多址通信系统的新型跳频序列族构造方法.该算法基于密码学的加密机制,具有好的安全性和高的计算复杂度;算法的设计遵循了密码学的"混淆"和"扩散"准则,生成序列具有各项优异的性能指标.本文从安全性、随机性、均匀性、复杂度、组网特性及跳频间隔特性等各方面对产生的跳频序列进行了全面的理论分析,证明该算法具有理想的综合系统性能指标.在此基础上,利用VHDL语言设计并开发出相应的跳频加密芯片.经测试其性能稳定、运算速度快、输入方式灵活多样,已应用于实际的高速跳频通信系统中.     

Performance of packet-switched fiber-optic frequency-hoppingmultiple-access networks

A packet-switched frequency-hopping multiple-access (FO-FHMA) communication system based on bus topology is proposed and investigated. In this arrangement, access to the optical medium for the network subscribers is provided via frequency-hopping (FH). The proposed FH technique in this analysis takes advantage of the Reed-Solomon (RS) codes to encode information packets and, consequently, to combat possible burst errors at the receiver. At user locations, encoded subpackets are frequency-hopped with the aid of a phase modulator, using a preassigned FH pattern for transmission over the optical medium. At the receiver site, a balanced phase discriminator/detection device followed by a frequency-dehopping receiver is used to recover the desired information. An alternative receiver structure, where the received signal is heterodyned prior to dehopping, is also proposed. The implications of this coherent detection are consequently discussed. Performance measures in terms of throughput and probability of incorrect decoding for chip synchronous model with asynchronous transmission characteristic in the absence of side information are obtained to assess the viability of the proposed packet-switched fiber-optic multiple-access communication system. Numerical results are presented when short RS codes are utilized as FH assignment codes     

An Internally Coded TH/OCDMA Scheme for Fiber Optic Communication Systems and Its Performance Analysis—Part I: Using Optical Orthogonal Code

In this paper, a new internally coded time-hopping optical code-division multiple-access (TH/OCDMA) scheme for fiber-optic communication systems is proposed, and its multiple-access performance is evaluated using optical orthogonal codes (OOCs). In the proposed method, the duration of each bit is divided into N_s frames, each one containing L chips. Two signature codes, namely, one pseudonoise (PN) sequence and one OOC, are assigned to each user. During each bit interval, based on the output of an channel encoder and the user's dedicated PN sequence, one of the N_s frames is selected, in which W pulses are transmitted in W chips, marked by the user's OOC. We consider three detectors at the receiver front end, namely, correlation, soft chip-level, and hard chip-level detectors. We evaluate the multiple-access performance of the system for each detector considering the effects of shot noise, dark current, and thermal noise. We compare the results with those obtained for the conventional OCDMA systems. Our numerical results indicate that, for the same bit rate and bandwidth, our proposed method substantially outperforms the conventional OCDMA system. Our results also show that the soft chip-level detector outperforms the other detection techniques in all cases considered     

Pulse Position Amplitude Modulation for Time-Hopping Multiple-Access UWB Communications

In this letter, we propose a new modulation scheme called pulse position amplitude modulation (PPAM) for ultra-wideband (UWB) communication systems. PPAM combines pulse position modulation and pulse amplitude modulation to provide good system performance and low computational complexity. The channel capacity of PPAM is determined for a time-hopping multiple-access UWB communication system. The error probability and performance bounds are derived for a multiuser environment.     

Throughput analysis of a slotted frequency-hop multiple-accessnetwork

A link throughput analysis is presented for a slotted frequency-hop multiple-access (FHMA) packet radio network (PRN) operating in the presence of background noise, partial-band noise jamming, and partial-band tone jamming. The PRN consists of an arbitrary number of transceivers arranged in a paired-off topology. Forward error-correction coding is used for packet protection. M-ary FSK modulation is used with hard-decision decoding. Expressions are derived for the link throughput in terms of the channel cutoff rate and capacity. The dependency of the optimal processing gain, code rate, and jamming fraction on the population size, traffic intensity, bit energy to background noise ratio, and bit energy to jammer noise ratio is examined in detail. It is shown that a properly designed (optimized) PRN using random-access FHMA offers a significantly larger heavy-load throughput than a random-access frequency-division multiple-access PRN     

Ultra-wide bandwidth time-hopping spread-spectrum impulse radio forwireless multiple-access communications

Attractive features of time-hopping spread-spectrum multiple-access systems employing impulse signal technology are outlined, and emerging design issues are described. Performance of such communications systems in terms of achievable transmission rate and multiple-access capability are estimated for both analog and digital data modulation formats under ideal multiple-access channel conditions     

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.     

Direct Blind Adaptive MOE Receiver for PAM Modulated Time-Hopping UWB System Over Frequency-Selective Fading Channel

Ultra wideband impulse radio systems have attracted great attention for their promised applications in high-speed short-range indoor wireless communication systems. Among the various modulation and multiple access schemes, this paper deals with time-hopping (TH) antipodal pulse amplitude modulation operating in the presence of a multipath fading downlink channel. We first employ a constrained optimization technique to design a batch mode blind (without exploiting training sequences and undesired users’ time-hopping (TH) codes) mobile station receiver. To reduce the computational complexity, we propose a blind adaptive receiver that is based on the criterion of maximizing the receiver’s minimum possible output energy. The algorithm jointly and iteratively optimizes the weight vector and channel impulse response to improve system performance. Simulation results show that the proposed adaptive receiver converges to the optimum batch mode receiver. Moreover, the algorithms are shown to be robust to multi-user interference and near-far problems.     

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     

Frequency-hopped multiple-access communications with multicarrier on-off keying in Rayleigh fading channels

We propose the multicarrier on-off keying (MC-OOK) as a bandwidth-efficient modulation method for frequency-hopped multiple-access (FHMA) communications. The motivation for using MC-OOK is that a more bandwidth-efficient modulation scheme allows a larger number of frequency slots, and thus provides a higher immunity against multiple-access interference in FHMA systems. We analyze the average bit-error probability in slow frequency-nonselective Rayleigh fading channels with background noise. We find that the capacity gain that MC-OOK/FHMA system provides over the MFSK/FHMA system in an interference-limited region is more than 2.5 when the modulation alphabet size M is 8, and even a higher capacity gain can be obtained with a larger M.     

Hit statistics in FH-CDMA unslotted packet networks

This correspondence is concerned with the statistical dependence of hits due to multiple-access interference in the time-unslotted frequency-hopping (FH) packet networks. Relying on the technique of joint probability generating functions (PGFs), we give a formal proof that if the ratio of the number of interfering packets to the number of frequency slots K/q is held constant, hits due to multiple-access interference are asymptotically independent as q/spl rarr//spl infin/. We also derive expressions for the correlation coefficients of hits in the packet.     

MPPSK调制的跳时多址研究

研究了一种MPPSK调制的跳时多址实现方法。发送端对时域连续的正弦载波进行调制,根据用户唯一分配的跳时图案及待发送的符号,在相应的时隙产生相位跳变,非跳变处都是正弦波;接收端将信号通过冲击滤波,依据传输时延及跳时图案获得相应时隙的包络值,进行检测判决。通过仿真,对比了相同调制参数下跳时多址MPPSK与非跳时MPPSK的误码性能。结果表明:在各用户跳时图案正交的情况下,跳时调制的MPPSK信号并未损失误码性能,验证了此种跳时多址实现方法的可行性和有效性。      

Well-structured FHMA codebooks: a geometric approach

A geometric approach in the design of codebooks for OR frequency-hopping multiple-access (FHMA) channels is developed by treating a signal matrix as a finite set of distinct points. The relationship among the parameters of an interference-free j-distinguishable-point codebook, j⩾1, is established by using coordinate-free arguments. Geometry induced by such a codebook is characterized, and the design of a well-structured j -distinguishable-point codebook is related to a block design problem. It is shown that a well-structured 1-distinguishable-point codebook implies the axiom system of a finite affine plane     

Optimum subpacket transmission for hybrid ARQ systems

Hybrid automatic-repeat-request (ARQ) is a flexible and efficient technique for data transmissions. In hybrid ARQ, subpacket schemes are more attractive for systems with burst errors than complete packet schemes. Although subpacket schemes were proposed in ARQ systems, optimum subpacket transmission is more effective to maximize throughput in a dynamic channel. Since convolutional codes have properties of burst errors in decoding, the optimum subpacket can be applied to convolutional codes. This paper investigates the performance of subpacket transmission for convolutionally coded systems. An efficient method is proposed to estimate the optimum number of subpackets, and adaptive subpacket schemes, i.e., schemes that enable a system to employ different optimum numbers of subpackets under various conditions, are suggested to achieve the maximum throughput of the system. Numerical and simulation results show that the adaptive subpacket scheme is very effective for the convolutionally coded hybrid ARQ system, and it can provide higher throughput, smaller delay,and lower dropping rate than complete packet schemes. Moreover, the adaptive subpacket scheme can be flexibly used with packet combining techniques to further improve the system throughput.     

Multiuser detection of time-hopping PPM UWB system in the presence of multipath fading

Ultra-wideband (UWB) impulse radio (IR) systems are currently being considered for several applications due to their attractive features that include low-power carrierless and ample multipath diversity. Among the various modulation and multiple-access schemes, time-hopping (TH) pulse position modulation (PPM) is a popular technique in application. Most past works rely on strict power control and perform single-user detection (matched filtering) on the desired signal. This paper aims to apply multiuser detection techniques in binary PPM (BPPM) UWB IR multiple-access systems. Moreover, we consider frequency-selective multipath fading channels to account for the wireless cellular environment. A class of linear multiuser detectors (LMDs) is applied to extract the information bits while eliminating multiuser interference (MUI) in the presence of multipath fading. Simulation results are provided to compare the performance of different LMDs.