Showing papers on "Spectral efficiency published in 1981"

Error rate performance of noncoherent detection of duobinary coded MSK and TFM in mobile radio communication systems

Abstract: Two continuous phase constant envelope modulation schemes are considered for use in digital mobile radio communication systems. These two schemes, duobinary coded minimum shift keying (MSK) and tamed frequency modulation (TFM), use partial response signaling to achieve efficient power spectrum. Therefore, they are suitable candidates for the application of digital data transmission via mobile radio where spectrum efficiency is an important consideration. The mobile communication channel is characterized by fast Rayleigh fading and cochannel interference resulting from the reuse of the channels. The error rate performance of duobinary coded MSK and TFM has been studied under these environments with noncoherent detection. A closed form expression for the probability of error of duobinary coded MSK with discriminator detection has been derived and evaluated for different cases of fast and slow fading and cochannel interference. The probability of error of duobinary coded MSK and TFM with differential detection has been calculated by numerical integrations for different cases of slow and fast fading and cochannel interference.

On the performance of phase-shift-keying systems

Abstract: Coherent phase-shift keying (CPSK) and differential phase-shift keying (DPSK) are widely used modulation methods in digital communications Bandwidth efficiency, good noise immunity, constant envelope, and simplicity of implementation make these schemes particularly attractive for use over the satellite, terrestrial radio and voiceband telephone channels While system analyses abound in the literature, treatment is usually restricted to the additive Gaussian channel Important issues determining ultimate performance, such as the joint effect of intersymbol interference and the acquisition of carrier phase have not been adequately addressed The main purpose of this paper is to develop analytical tools that can be used to assess system performance under practical operating conditions Pure coherent demodulation schemes such as CPSK are ideals which are rarely achieved in practice, and carrier phase must be estimated prior to and/or during data transmission This requires start-up time, as well as added equipment, and the fidelity of the phase estimate ultimately determines performance In contrast, DPSK is independent of carrier phase, since decisions are made on phase differences However, this comes at a price, and it is known that ideal multiphase DPSK suffers an asymptotic performance penalty of 3 dB in signal-to-noise ratio (s/n) over ideal CPSK We develop a new rigorous method for calculating the error rates of both CPSK and DPSK, under a variety of operating conditions In particular, we find that the intersymbol interference penalty for quaternary DPSK is about 1 dB worse in s/n than for CPSK We demonstrate that the detection efficiency of CPSK approaches the ideal, provided that the s/n of the phase-recovery circuit is about 10 dB more than that at the receiver input Alternatively, for the same s/n, a 10-baud phase-locked loop integration time is required to achieve near-ideal performance

Improvements in use of congested spectrum for land mobile radio service by adoption of bandsharing spread-spectrum system with TV broadcast channels

Abstract: The paper examines the possibility of private mobile radio users sharing the RF spectrum with the television broadcast channels on a mutual noninterference basis, with the aim of accommodating greater spectrum efficiency. A comparison is made between the use of conventional narrowband modulation methods, such as AM, FM and SSB, and the broadband direct-sequence spread-spectrum modulation schemes as contenders for a bandshared system. These comparisons are made using the criteria for establishing imperceptible visual interference on the TV screen for both modulation schemes. The results show that, for a base station sited in Central London with a service area typically that of the Greater London region, 16 MHz of bandwidth may be gained by the use of bandsharing, with either narrowband or spread-spectrum modulation schemes, for guaranteed interference-free TV reception. The paper also shows that, for the same base-station site covering the same area, a further 72 MHz of bandwidth could be opened up by the use of direct-sequence spread-spectrum transmissions, which would otherwise be unavailable for narrowband use. Such a system would also have the advantage that it could be made covert to eavesdroppers using conventional AM or FM receivers with only limited modification to existing transmitters and receivers, It is argued that spread-spectrum techniques can open up significant amounts of bandwidth, by bandsharing, not available to conventional modulation schemes in many urban environments where the normal TV-channel allocations are almost fully utilised, as they appear to be in the Greater London area.

Channel assignment schemes and traffic capacities of mobile radio systems

Abstract: In this paper, we examine the spectrum efficiency of various land mobile radio system approaches in terms of traffic capacity for a given number of channels. Spectrum Efficiency can also be described in terms of Communication Capacity of the system per unit bandwidth. To determine the number of users a system can support for a given grade of service, both aspects (traffic handling and communication) should be considered simultaneously. In the first part of this paper we examine the traffic capacity of cellular mobile radio systems with different channel assignment schemes. It is shown that cellular systems are superior to trunked systems with moderate frequency reuse but not without frequency reuse. However, with use of effective channel assignment schemes, cellular system's performance is close to that of trunked systems even without frequency reuse. Adaptive channel assignment schemes are examined. Adaptive shcemes are based on the fact that traffic intensity of the arrival process varies slowly with time. Therefore, channels can be assigned to take the maximum advantage of the random nature of the arrival process and the frequency reuse at a given time. Traffic capacity of the mobile radio system is examined which uses the same set of channels to service the different classes of users. One such example is the mobile radio system which provides voice-telephone and dispatch service on the same channels. Arrival process is assumed to be Poisson for both telephone and dispatch calls with different arrival rates. Service rates are also different for the telephone and dispatch calls. Blocked telephone calls are cleared from the system and blocked dispatch calls are delayed. Another example is a mobile radio system which services different classes of users with different service times and grades of service.

Error rate performance of duobinary coded MSK and TFM with differential detection in land mobile communication systems

Abstract: Two continuous phase constant envelope modulation schemes are considered for use in digital mobile radio communication systems. These two schemes: duobinary coded MSK and tamed frequency modulation (TFM) use partial response signaling to achieve efficient power spectrum. Therefore, they are suitable candidates for the application of digital data transmission via mobile radio where spectrum efficiency is an important consideration. The mobile communication channel is characterized by fast Rayleigh fading and cochannel interference resulting from the reuse of the channels. The error rate performance of duobinary coded MSK and TFM has been studied under these environment with differential detection. The probability of error has been calculated by numerical integrations for different cases of slow and fast fading and cochannel interference.

Direct sequence spread spectrum techniques for land mobile radio applications

Abstract: This thesis describes an investigation into the application and performance of direct sequence spread spectrum techniques for land mobile radio systems. There is a brief description of the basic principles of operation of direct sequence systems. The multiple user facility is analysed and values obtained for the maximum number of simultaneous system users in terms of system parameters. This clearly illustrates the need for power control. A possible method of providing power control is described. Comparison of user density is made against conventional narrowband modulation methods. There is some discussion of the effect of sequence cross-correlations on the number of system users. The system organisation is mentioned, showing possible application of a calling channel. Consideration is given to the possibilities of bandsharing with narrowband modulation systems. Figures are derived for the resulting interference to existing systems which would be caused by such an arrangement. A brief resume of the pertinent features of the land mobile radio channel is given. The effects of shadowing on the output quality and spectral efficiency of direct sequence systems is discussed. There is an analysis of the effects of shadowing on the user density in small cell schemes. An analysis shows the effects of multipath propagation on direct sequence performance by reference to a simple two path channel. Details are given of a simple experimental direct sequence spread spectrum transmitter and receiver constructed. The measured results for the performance of the system against various forms of interference and channel degredation are compared with their theoretical values. Finally ideas for future work are discussed.