Transmitter diversity for a digital FM paging system

Multipath fading is one of the most serious problems for the signal transmission in mobile radio. To combat this problem, the application of transmitter diversity to a digital FM paging system is described. The method is to transmit two digital FM paging signals with different modulation indices, each of which is modulated by an identical binary signal, from separate antennas. It is shown that the same action obtained with the well-known selection diversity can be achieved when the difference between the modulation indices is equal to two. The diversity effect on the bit-error-rate (BER) performance is theoretically analyzed. The diversity effect on the BER performance in a 600-bit/s Manchester-coded digital FM system is verified by the laboratory simulation tests using a Rayleigh fading simulator.     

Performance of 16 kbit/s GMSK transmission with postdetection selection diversity in land mobile radio

Through laboratory simulation tests and field experiments in the Tokyo metropolitan area, 16 kbit/s Gaussian filtered minimum shift keying (GMSK) transmission performance has been experimentally clarified in the 920 MHz land mobile radio environment. The experimental results agree closely with theory, and they show that fast multipath fading severely degrades average bit error rate (BER) performance in GMSK transmission. However, a space diversity reception technique using a postdetection selection combining scheme is able to efficiently mitigate the fast multipath fading.     

Field test measurement for 128 kbit/s QPSK signal transmission and delay time spread in 1.5 GHz-band land mobile radio

High-speed digital signal transmission is a promising new field of communication services. In land mobile radio communication, transmission quality severely suffers from frequency selective fading under multipath radiowave transmission environments. Field test measurement results for 128 kbit/s QPSK signal transmission and delay time spread in the Tokyo metropolitan area are presented. The two-branch diversity reception method was adopted to combat fading. Bit error rate (BER) performance is obtained as a function of delay time spread.<>     

Performance of 16 kbit/s GMSK Transmission with Postdetection Selection Diversity in Land Mobile Radio

Through laboratory simulation tests and field experiments in the Tokyo metropolitan area, 16 kbit/s Gaussian filtered minimum shift keying (GMSK) transmission performance has been experimentally clarified in the 920 MHz land mobile radio environment. The experimental results agree closely with theory, and they show that fast multipath fading severely degrades average bit error rate (BER) performance in GMSK transmission. However, a space diversity reception technique using a postdetection selection combining scheme is able to efficiently mitigate the fast multipath fading.     

QDPSK signal transmission performance with postdetection selectiondiversity reception in land mobile radio

The bit error rate (BER) performance of 16-128 kb/s Nyquist raised-cosine filtered quaternary differential phase-shift keying (RC-QDPSK) signal transmission was experimentally investigated. Two-branch postdetection selection diversity reception was employed. Measured results are presented for the BER performance due to additive white Gaussian noise (AWGN), cochannel interference, and multipath channel delay spread. Field BER measurements were also conducted at a carrier frequency of 1.45 GHz in an area characterized by high-rise buildings and in an area surrounded by mountains. The results show that postdetection selection diversity is a simple yet powerful technique to improve the BER performance in fading mobile radio channels     

Performance of a new adaptive diversity-equalisation for digital mobile radio

A new adaptive diversity-equalisation suitable for mobile radio signal transmission in the mobile radio fast fading environment is proposed. Adaptivity of the diversity-equalisation is enhanced by employing the recursive least-squares algorithm (RLS) with exponential weighting and two newly proposed techniques: bi-directional equalisation (BDE) and transmitter time-diversity (TDD). Computer simulation shows that QPSK transmission performance equivalent to that of four-branch diversity can be obtained with small impairment.<>     

Transmitter diversity effect in TDMA/TDD mobile radio transmission

Transmitter diversity, which employs a single transmit/receive antenna at the portable stations and two transmit/receive antennas at the base station, is experimentally investigated for a TDMA/TDD (time division duplex) mobile radio system. Experimental results show that transmitter diversity can significantly improve the BER (bit error rate) performance of the portable station, due to AWGN (additive white gaussian noise), delay spread, and CCI (cochannel interference) in Rayleigh fading environments.<>     

Probability of error analysis of digital partial responsecontinuous phase modulation with two-bit differential detection andoffset receiver diversity in fast Rayleigh fading channels

The performance of constant envelope digital partial response continuous phase modulation (PRCPM) with two-bit differential detection and offset receiver diversity is theoretically analyzed in fast Rayleigh fading channels. A simple closed-form expression for the probability of error is derived and evaluated for cases of practical interest to researchers and designers of land mobile radio systems. It is shown that the dynamic bit error rate (BER) performance is considerably improved using the offset diversity scheme. Thus, many PRCPM signals having a compact power spectrum can be used in future digital mobile radio systems     

Design and Test of a Spectrally Efficient Land Mobile Communications System Using LPC Speech

A communication system was built and tested to operate in the land mobile VHF band (150-174 MHz) at a channel separation of only 6 kHz. The audio source was digitally encoded at 2.4 kbits/s using linear predictive coding (LPC). The speech data stream was transmitted by frequency shift keying (FSK) which allowed the use of class-C transmitters and discriminator detection in the receiver. Baseband filtering of the NRZ data resulted in a narrow transmitter spectrum. The receiver had a 3 dB bandwidth of 2.4 kHz which allowed data transmission with minimal intersymbol interference and frequency offset degradation. A 58 percent eye opening was found. Bit error rate (BER) performance was measured with simulated Rayleigh fading at typical 150 MHz rates. Additional tests included capture, ignition noise susceptibility, adjacent channel protection, degradation from frequency offset, and bit error effects upon speech quality. A field test was conducted to compare the speech quality of the digital radio to that of a conventional 5 kHz deviation FM mobile radio.     

OFDM for data communication over mobile radio FM channels. I.Analysis and experimental results

The performance of OFDM/FM modulation for digital communication over Rayleigh-fading mobile radio channels is described. The use of orthogonal frequency division multiplexing (OFDM) over mobile radio channels was proposed by Cimini (1985). OFDM transmits blocks of bits in parallel and reduces the bit error rate (BER) by averaging the effects of fading over the bits in the block. OFDM/FM is a modulation technique in which the OFDM baseband signal is used to modulate an FM transmitter. OFDM/FM can be implemented simply and inexpensively by retrofitting existing FM communication systems. Expressions are derived for the BER and word error rate (WER) within a block when each subchannel is QAM-modulated. Several numerical methods are developed to evaluate the overall BER and WER. An experimental OFDM/FM system was implemented and tested using unmodified VHF FM radio equipment and a fading channel simulator. The BER and WER results obtained from the hardware measurements agree closely with the numerical results     

Design and test of a spectrally efficient land mobile communications system using LPC speech

A communication system was built and tested to operate in the land mobile VHF band (150-174 MHz) at a channel separation of only 6 kHz. The audio source was digitally encoded at 2.4 kbits/s using linear predictive coding (LPC). The speech data stream was transmitted by frequency shift keying (FSK) which allowed the use of class-C transmitters and discriminator detection in the receiver. Baseband filtering of the NRZ data resulted in a narrow transmitter spectrum. The receiver had a 3 dB bandwidth of 2.4 kHz which allowed data transmission with minimal intersymbol interference and frequency offset degradation. A 58 percent eye opening was found. Bit error rate (BER) performance was measured with simulated Rayleigh fading at typical 150 MHz rates. Additional tests included capture, ignition noise susceptibility, adjacent channel protection, degradation from frequency offset, and bit error effects upon speech quality. A field test was conducted to compare the speech quality of the digital radio to that of a conventional 5 kHz deviation FM mobile radio.     

A periodic switching diversity technique for a digital FM land mobile radio

A simple and efficient diversity technique is proposed for use in a digital FM land mobile radio communication system. This technique receives two RF signals periodically by switching two antenna branches at a rate moderately higher than the bit rate. The improved bit error rate (BER) performance resulting from the use of diversity is shown to be the effect of transforming the probability density function of the signal energy per bit to noise power density ratio to a sharper distribution. Laboratory simulation test results show that in a Manchester-coded frequency-shift keying (FSK) system with a bit rate of 600 bit/s and a frequency deviation of ±5 kHz, the diversity gain at an average BER of 1 × 10^-3is about 10 dB for an optimum switching rate of about 2 kHz. This diversity improvement is also verified by the field test performed in a suburban area.     

多用户SIMO-OFDM系统中的协作分集性能分析

协作分集使得在多用户环境下,具有单天线的多个终端可以共享彼此的天线,以形成一个虚拟的天线阵列结构,实现空域分集。首先介绍了多用户SIMO—OFDM系统中的两种协作方式,放大前传和译码前传。然后针对源结点和目的结点之间是否存在路径损耗,提出了一种基于信道状态信息的选择中继协作方式,并对系统性能进行了理论和仿真分析。仿真结果表明,这种基于信道状态信息的选择中继协作方式可以获得较好的系统性能。     

A comparison of specific space diversity techniques for reduction of fast fading in UHF mobile radio systems

Over the past few years a variety of space diversity system techniques have been considered for the purpose of reducing the rapid fading encountered in microwave mobile radio systems. Basic diversity methods are first reviewed in the framework of mobile propagation effects, and then specific techniques are compared from the standpoint of transmitter power required to achieve a certain performance. Criteria of comparison used included baseband SNR while moving and reliability when the vehicle stops at random. System parameters are type and order of diversity and transmission bandwidth. Tradeoffs between performance properties and system parameters are indicated. The calculations show that relatively modest use of diversity techniques can afford savings in transmitter power of 10-20 dB. For example, at a range of 2 mi, to obtain 30-dB baseband SNR while moving and 99.9-percent reliability when stopped requires a transmitted power of 8 W for a conventional FM system with no diversity. Two-branch selection diversity provides the same performance for a transmitter power of only 300 mW.     

Matched-Filter Bounds for Multicarrier Communications Systems With Transmit Diversity

In this paper, we consider wireless multicarrier communications systems applying different transmit-antenna diversity techniques. Whereas the transmitter has available multiple antennas, we assume a single antenna at the receiver. Thus, we consider multiple-input single-output multicarrier transmission systems which are of special interest for downlink mobile radio applications. For these systems, we investigate the matched-filter bounds (MFBs) which represent the performance in an environment free of any interference and, thus, are lower bounds on the achievable performance. Especially, we focus on the analytical determination of the MFBs for selection diversity (SD), since this transmit-antenna diversity technique requires the least amount of preprocessing at the transmitter. Based on the derived MFBs, SD is investigated in detail, and compared with other transmit-antenna diversity techniques which are based on the maximum-ratio and the equal-gain transmission principles, respectively.     

Generalized Tamed Frequency Modulation and Its Application for Mobile Radio Communications

Continued investigation of tamed FM (TFM) has led to an extension called generalized tamed FM (GTFM). The very narrow spectral property of a GTFM signal meets the stringent requirements on bandwidth utilization in modern mobile radio applications. The principle of GTFM is first described. It is then shown that the generation of GTFM signals can be made very simple by the use of an ROM table-lookup technique. By an appropriate choice of parameters in GTFM signal generation at the transmitter, a joint optimization for coherent and noncoherent detection with regard to BER performance in the presence of additive white Gaussian noise can be achieved. For mobile radio applications, the robustness of the detection scheme to fast fading is important. A low-complexity noncoherent receiver is presented, Comprising a frequency discriminator and a simple maximum-likelihood sequence estimator. This receiver performs well in a fast fading environment. Computer simulated results of BER performance of this scheme are given. These results are confirmed by experimental measurements.     

Generalized tamed frequency modulation and its application for mobile radio communications

Continued investigation of tamed FM (TFM) has led to an extension called generalized tamed FM (GTFM). The very narrow spectral property of a GTFM signal meets the stringent requirements on bandwidth utilization in modern mobile radio applications. The principle of GTFM is first described. It is then shown that the generation of GTFM signals can be made very simple by the use of an ROM table-lookup technique. By an appropriate choice of parameters in GTFM signal generation at the transmitter, a joint optimization for coherent and noncoherent detection with regard to BER performance in the presence of additive white Gaussian noise can be achieved. For mobile radio applications, the robustness of the detection scheme to fast fading is important. A low-complexity noncoherent receiver is presented, comprising a frequency discriminator and a simple maximum-likelihood sequence estimator. This receiver performs well in a fast fading environment. Computer simulated results of BER performance of this scheme are given. These results are confirmed by experimental measurements.     

Performance analysis of a time diversity ARQ in land mobile radio

A time diversity automatic repeat-request (ARQ) scheme with a finite number of transmissions is investigated for a digital FM mobile radio with frequency demodulation (FD). It processes all the retransmissions of a single data block using postdetection diversity combining. The analysis of the signal energy per bit required for a given bit error rate (BER) and the spectral efficiency in a cellular mobile radio system are presented. The results obtained from the numerical calculations show that this ARQ scheme offers a performance superior to both the basic ARQ scheme and the time-diversity scheme     

Optimised secure transmission through untrusted AF relays using link adaptation

A new transmission scheme is presented for a two-hop relay network including two AF relays, considering physical layer security where relays are not able to detect signal with an acceptable bit error rate (BER) but the combined received signal is detected with an acceptable BER at the final receiver. It is assumed that there is no direct path between the transmitter and the receiver (relay network without diversity). Adaptive modulation and coding is utilised at the transmitter and transmission powers of the transmitter and of the relays are continuously adapted provisioning individual average power constraint for each node. Numerical evaluations show that an acceptable performance degradation is seen by the proposed secure relaying scheme compared to the optimum relay selection scheme without security constraint.     

Analysis of TCP performance under joint rate and power adaptation in cellular WCDMA networks

To improve the spectral efficiency while meeting the radio link level quality of service requirements such as the bit-error-rate (BER) requirements for the different wireless services, transmission rate and power corresponding to the different mobile users can be dynamically varied in a cellular wideband code-division multiple-access (WCDMA) network depending on the variations in channel interference and fading conditions. This paper models and analyzes the performance of transmission control protocol (TCP) under joint rate and power adaptation with constrained BER requirements for downlink data transmission in a cellular variable spreading factor (VSF) WCDMA network. The aim of this multilayer modeling of the WCDMA radio interface is to better understand the interlayer protocol interactions and identify suitable transport and radio link layer mechanisms to improve TCP performance in a wide-area cellular WCDMA network.