BPSK system with sounder to combat Rayleigh fading in mobile radio communication

A simple method is proposed to remove random FM from a fast Rayleigh faded binary phase shift keying (BPSK) signal and the great improved performance of reducing the irreducible error is presented. In the mobile radio environment, there happens inevitably a fast Rayleigh fading which causes random FM. The phase error of the reference signal due to random FM will degrade the bit error rate (BER) performance, even if the signal-to-noise ratio is sufficiently high. In the realization of reliable mobile communication, removal of this random FM is an unavoidable theme. Proposed strategy is to transmit a sounding continuous wave (CW) together with a BPSK signal, each phase being kept orthogonal and each power being kept the same. This CW wave is also used as the reference signal in coherent reception. The BER performance of this system is worse by 3 dB than that of the coherent BPSK in a slow Rayleigh fading environment.     

Using RF filtering to reduce competitor-induced interference

This paper examines the success of RF filtering on mitigating interference that occurs between two wireless multiple-access systems operating within the same geographic area. Such interference is referred to as "competitor-induced interference" and can significantly degrade system capacity and performance. Three dual-system scenarios are considered: a dual code-division multiple-access (CDMA) (IS-95) system, a CDMA mobile in an FM (AMPS) cell, and an FM mobile in a CDMA cell     

Transmission scheme of high-capacity FM multiplex broadcastingsystem

FM multiplex broadcasting is a system for providing additional text and graphics, while maintaining compatibility with existing stereo sound broadcasting. The digital signals are multiplexed in a higher frequency band than baseband FM stereo signals. This paper describes a modulation method and an error correction method for a new high-capacity FM multiplex broadcasting system called DARC (Data Radio Channel), which has a bit rate of 16 kbit/s. Simulation results show that stereo sound signals interfere with a multiplexing signal under multipath conditions. LMSK (level controlled MSK) is proposed as a modulation scheme to ensure good transmission quality. It is shown that an error correction scheme using a product code of (272190) codes has a good performance for mobile reception. Field tests on the DARC for mobile reception are conducted in the service area of the NHK Tokyo FM station. These show that the correct reception rate can be obtained at more than 80% when transmitting information of 6 kbytes     

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.     

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     

An efficient baseband modem technique for data transmission overanalog FM links

In mobile radio where data are transmitted over existing analog FM systems, the receive bandpass bandwidth, which is adapted to the analog speech transmission, is larger than would be required by data transmission. This results in poor error performance. A novel baseband modem technique which drastically improves the error performance is proposed and analyzed. A smearing filter is used to convert the compound baseband noise at the limiter discriminator output to approximately Gaussian noise. This optimizes the performance at large carrier-to-noise ratios (CNRs). A baseband click detection and elimination scheme, which improves the performance at small CNR is proposed. Simulation results show that this system requires 3.8 dB less CNR than the conventional digital FM system to achieve a bit error probability of 10^-4. It is concluded that the technique is attractive for data transmission over analog FM links     

On the use of Reed-Solomon codes in improving digital FMtransmission performance in Rayleigh fading

Reed Solomon codes with interleaving are used in a binary FM transmission affected by Rayleigh fading as encountered in land mobile radio. A new decoding algorithm is proposed which can be implemented in simple hardware. The error performance of the binary FM system with the RS code with one and two degrees of interleaving is measured. A significant reduction of error rate floor as a function of fading speed is noted and discussed     

Is FM a RF-Based Positioning Solution in a Metropolitan-Scale Environment? A Probabilistic Approach With Radio Measurements Analysis

Recent mobile devices have already contained a low-cost FM receiving function due to the continuing improvements in the device manufacturing. This paper shows that positioning based on FM signal is an alternative radio option while meeting the FCC requirement. We present a probabilistic location system using a wider-covered and longer-lived FM infrastructure. The performance is evaluated in two different metropolitan-scale environments including National Taiwan University (NTU) and Wen-Shan rural area. Both results show that the FM based location system not only satisfies the FCC requirement but also provides a comparable or even better performance to GSM based solution. Moreover, we completely analyze the realistic radio measurements of FM and GSM from four perspectives including temporal variation, spatial separation, measurement correlation and spectrum allocation. Most FM measurements are observed to provide a lower temporal variation but a weaker spatial separation than GSM. Fortunately, we discover that the lack of spatial separation can be compensated by adding additional sensed channels. This property is useful especially for a rural area where the available GSM base stations are limited and distant. Furthermore, we point out that the spatial separation of GSM signal decreases when the signal level is weaker than $-$ 90 dBm. At such a condition, FM reports a better accuracy than GSM even with the fewer channels.      

Error rate performance of digital FM mobile radio withpostdetection diversity

An analysis of bit error rate (BER) in a binary digital FM system with postdetection diversity is presented. Expressions for the average BER due to additive white Gaussian noise (AWGN), random FM noise and delay-spread in the multipath channel are derived for reception using differential demodulation (DD), and frequency demodulation (FD) assuming independent fading signals. Calculated results for MSK show that the BER performance is strongly dependent on the RMS-delay/bit-duration ratio and that the delay-spectrum shape is of no importance when the receiver predetection filter product is optimized for the effect of AWGN. The effect of fading correlation on the diversity improvement is also analyzed for a two-branch case with multiplicative Rayleigh fading signals. Expressions for the average BER due to AWGN and random FM noise are derived. Calculated results are shown for the average BER due to random FM noise assuming a horizontally spaced antenna system at a mobile station. It is shown that the use of small antenna spacings leads to a diversity improvement greater than that obtainable for the case of independent AWGN     

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     

Analysis of multiplex techniques for land mobile radio service

Two types of frequency multiplexing are theoretically analyzed for their applicability as a form of modulation in the land mobile radio service (LMRS). Both SSB/FM and FM/FM are analyzed for their signal-to-noise ratio (SNR) versus modulation index. These results are normalized to the signal-to-noise performances of the existing 5-kHz deviation system for comparison purposes. The latter performance is developed using the actual Electronic Industries Association (EIA) response of a LMRS receiver. The spectrum of the multiplex system for the case of equal subchannel signal-to-noise is developed using a computer. The spectrum is used to determine the spectrmm occupancy of multiplex systems. Based on the tradeoffs of transmit power and spectrum occupancy, a discussion of the interference characteristics of the multiplex systems compared to the existing system is presented. Finally, conclusions are drawn on the spectrum efficiency of a multiplex system compared to the present system.     

OFDM for data communication over mobile radio FM channels. II.Performance improvement

For pt.I see ibid., vol.39, no.5, p.783-93 (1991). The performance of an orthogonal frequency-division multiplexing (OFDM)/frequency modulation (FM) system for data communication over Rayleigh-fading mobile radio channels was analyzed in pt.I. The effects of forward error correction, switching diversity, automatic gain control (AGC), and squelch are studied. It is shown that OFDM/FM works well with switching diversity because OFDM can average out the transients created by switching between antennas. It is also found that the independent error assumption can be used to predict the distribution of the number of errors in a word. The use of squelch produced a small (about 1 dB) performance improvement, whereas the use of AGC provided negligible improvement     

A novel demodulator/detector for digital and analog signals on LMRchannels

The design, implementation, and performance of an all-digital demodulator/detector suitable for differential phase-shift keying (DPSK), continuous-phase frequency-shift keying (CPFSK), frequency-shift keying (FSK), and analog FM are discussed. In this modulator/detector, two detectors, one noncoherent and another differentially coherent, operate simultaneously to provide data detection and automatic frequency control (AFC). Test results indicate that the system provides improved performance over the conventional analog quadrature detector for two-period raised-cosine (2RC) CPFSK modulation in additive white Gaussian noise (AWGN) and Rayleigh fading channels. Being all-digital, the demodulator/detector is well suited for integrated circuit implementation. In addition, the system performs as well as the analog quadrature detector for analog FM voice transmissions, thereby maintaining full compatibility with analog land mobile radio (LMR) transmissions     

OFDM/FM frame synchronization for mobile radio data communication

A synchronization scheme enabling the use of orthogonal frequency division multiplexing (OFDM)/FM over a mobile radio channel in a pure ALOHA environment is proposed. The scheme encodes synchronization information in parallel with data in the same manner in which data is encoded in the OFDM/FM frame. The synchronization information is in the form of tones, centered in certain reserved frequency subchannels of the OFDM signal. The receiver uses a correlation detector, implemented in the frequency domain, to acquire synchronization accurately on a packet-by-packet basis. Experimental results indicate that the bit-error-rate performance achievable with the proposed scheme is within 1.5 dB of the performance obtained with ideal synchronization     

SSB versus FM at VHF for mobile radio telephony

Results from a comparison of SSB and FM for telephony use in mobile radio are reported. The tests were conducted at carrier frequencies of about 160 MHz, and the impairments considered included ignition noise, fading and cochannel interference. The results show the subjective performance of SSB to be poorer than that of 12.5 kHz FM.     

Digitized speech transmission at VHF using existing FM mobile radios

An extensive study of digitized speech transmission over existing VHF FM mobile radio sets is presented. Objective criteria expressed in terms of bit error rate (BER) are determined for the performance evaluation of analog FM radios when transmitting digital voice. These criteria are used to define the technical characteristics such as the receiver sensitivity, co-channel rejection, and adjacent channel selectivity in the case of digital FM transmission. The concept of performance measurements of existing sets in the digital mode of operation is suggested. The results of performance measurements reported here include the following: 1) radiated FM spectra, 2) bit error rate curves, 3) receiver sensitivity, 4) BER performance in the presence of analog or digital FM interference on the same or adjacent channel, 5) signal plus noise plus distortion to noise plus distortion ratio (SINAD) performance in the presence of co-channel or adjacent channel interference for both types of interfering signals, 6) co-channel rejection and adjacent channel selectivity for various combinations of the wanted and interfering signals, 7) receiver selectivity for both modes of operation, and 8) adjacent-signal selectivity for various combinations of the desired and undesired signals. Optimum values of design parameters of digital voice radio system are deduced from the obtained results. Finally, the implications of digitized speech transmission on the technical characteristics, operating range, channel reuse distance, and adjacent channel interference performance of analog FM radios are discussed.     

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.     

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.