Packet switching in digital cellular systems

Direct sequence (DS) code-division multiple-access (CDMA) is a modulation and multiple access technique currently being implemented in digital cellular mobile radio communication systems. The conventional quasisynchronous (QS) DS-CDMA communication system is generalized, and the problem of optimal spreading pseudonoise (PN) sequence design for new QS DS-CDMA communication systems is formulated. The classes of optimal PN sequences which have good pseudo-randomness and very small cross-correlation values for some range of offsets are designed by using a matrix-based approach. In contrast to the case of the other sequences, the optimal PN sequences produce small multiple-access interference (MAI) which is not affected by the number of users if there are sufficiently large number of users in the link. The new results are compared with the commonly used PN sequences to prove the superiority of our designed sequences, and the system performance of the QS-CDMA systems using different PN sequences are also evaluated.

The bit error rate (BER) performance of digital cellular radio systems was investigated in a Nakagami (1960) fading, correlated lognormal shadowing and additive white Gaussian noise (AWGN) environment for noncoherent differential phase shift keying (DPSK) modulation. Two models were used to determine the BER; the first one is based on the cumulative power levels of cochannel interferers while the second one is based on instantaneous cochannel interference power. The relative advantages of the two models were presented for various design parameters. The effects of bit energy to noise ratio, frequency reuse distance, cluster size, correlation coefficient, shadow spread, and fading parameter were studied. The BER was observed to be lower in a correlated shadowing environment compared with the uncorrelated case. The near-far effect was studied by assuming that both the desired and interfering mobiles are randomly located in their corresponding cells.

An integrated circuit for the Pan-European Groupe Speciale Mobile (GSM) digital radio systems is described which performs the modulation and front-end functions for both base and mobile stations. The circuit, fabricated using a 2- mu m CMOS technology, fully meets the GSM requirements. The system uses Gaussian minimum-shift keying (GMSK) modulation, with a 0.3 modulation index, which is characterized by a narrowband spectrum. The circuit dissipates 180 mW with a single 5-V supply. The die size is 6.7 mm*5.3 mm.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In the last chapter, the use of established analogue modulation techniques was described in the context of high-capacity cellular radio telephone applications. Conclusions regarding existing systems operation and future developments may be drawn, and these centre on the issue of capacity. Already, first-generation systems are showing signs of capacity saturation in major urban centres, even with a relatively modest total user population. Clearly, major capacity increase will be called for to meet future demand, and second-generation systems must address this challenge. What are the options available? To extend existing system operations, more spectrum would have to be made available. Alternatively, new approaches to system design must be found to utilize spectrum more efficiently.

A digital tanlock loop (DTL) is a nonuniform sampling digital phase-locked loop (DPLL) whose phase error detector, using the tan/sup -1/[/spl middot/] function with in-phase and quadrature samples of incoming signal, has a linear characteristic with a period of 2/spl pi/. In this paper, we study the application of an N-phase DTL in digital cellular radio with /spl pi//4-DQPSK modulation. The performance degradation due to fading effect is investigated in terms of bit error rate and steady state phase error variance by computer simulation. It is shown that, in the digital cellular radio system, the performances on both bit error rate and phase error variance using DTL are far better than that using the traditional digital N-phase I-Q loop.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A study has been under way in the UK for a number of years examining the potential for harmonious coexistence between ISM (industrial, scientific and medical) equipment operating within or outside the 900 MHz ISM bands (896 and 915 MHz) and cellular radio systems. The equipment primarily under consideration has been high-power magnetron-based microwave heating equipment, and the effects on both analogue and digital cellular systems have been assessed (Kenington and Bennett, 1993). The previous work has been concerned with the protection ratio afforded to these cellular systems by accurately simulated ISM signals, generated in a laboratory environment. The authors describe the final phase of the work, which involved performing field measurements around a number of different ISM installations in widely differing locations around the UK. These measurements were performed to assess the current levels of emissions from ISM equipment and the form of the ‘radiation pattern’ of typical installations. From this it is possible to estimate areas of potentially poor cellular reception, based on the previously derived protection ratios and assumptions about the location of the nearest base station. This work has been carried out, in part, to help explain the very low number of incidences of interference between ISM equipment and cellular radio equipment, despite the high emission limits set for this equipment in the UK (120 dBµV/m at 30 m from the wall of the building housing the equipment).

Mid‐entry strategy is an R&amp;D strategy designed for an efficient utilisation of scientific and technological resources across the nations. It chooses the entry point of R&amp;D projects in the mid‐stage of technical development. The technological situation of developing countries compels them to choose the mid‐entry strategies tailored to specific technologies. The development of the CDMA (Code Division Multiple Access) based digital cellular mobile communication system by ETRI, Korea’s government‐sponsored research institute, is an example showing the application of this strategy. ETRI utilised scientific resources owned by US based Qualcomm Ltd and co‐operated with local companies for the development. In the first half of 1996 the successful commercialisation of the CDMA digital cellular telephone service was launched in Korea, ahead of all other countries. Two Korean mobile communications providers have adopted the system.

Outlines the requirements for the various digital signal processing functions of the pan-European digital mobile cellular telephone system in terms of computational power and RAM and ROM capacities, and describes a digital signal processor (DSP) solution which is able to integrate all of these digital baseband functions for a hand-held terminal onto one VLSI chip. The KISS-16V2 processor, a low-power CMOS 16-b DSP, is optimized for digital telecommunications, especially for Groupe Speciale Mobile (GSM). A power-down mode together with the capability of memory and multiplier standby operation make this DSP well suited for handheld devices. A design strategy based on the extensive use of cell compilers and synthesis tools reduces the design of further DSP derivations to a minimum. >

A digital cellular mobile radio system has been under development in Europe since 1982 under the coordination of the working group CEPT GSM (groupe speciale mobile). In a recent coordinated experiment, listening opinion tests were performed on the speech output of six candidate 16 kb/s speech coding schemes for this system: one regular-pulse excited coder, one multiple-excited coder, and four subband coders. For comparison purposes, test conditions from a companded cellular FM system currently in operation were included in the experiment. The six codecs were companded in terms of subjective quality, transmission delay, and ease of implementation. In this overall comparison, no single codec was superior in all respects. However, the regular-phase-excited linear predictive coder, which provided the best speech quality, had acceptable complexity and delay and was singled out for further improvement. Ultimately, an improved version of this codec, a regular-pulse-excited/long-term-prediction LPC coder was selected. >

One of the critical and costly components in digital cellular communication systems is the RF power amplifier. Theoretically, one of the main concerns in an RF power amplifier design is the nonlinear effect of the amplifier. Quantitatively, no explicit relationship or expression currently exists between the out-of-band emission level and the nonlinearity description related to the third-order intercept point (IP/sub 3/). Further, in experiments and analysis, it was discovered that, in some situations, using IP/sub 3/ only is not accurate enough to describe the spectrum regrowth, especially when the fifth-order intercept point (IP/sub 5/) is relatively high compared to the third-order intermodulation. We analyze the nonlinear effect of an RF power amplifier in CDMA (IS-95 Standard), TDMA (IS-54 Standard) and MIRS M-16-QAM (Motorola integrated radio system standard) systems, give expressions for the estimation of the out-of-band emission levels for each system expressed by power spectrum, in terms of the IP/sub 3/ and the IP/sub 5/, as well as the power level of the signal. This result may be useful in the design of RF power amplifiers for these wireless communication systems.

Digital cellular communication systems in urban areas are today beginning to be limited in performance by interference. To further increase the capacity in these areas, more advanced detection schemes could be used. We study how the performance of the MLSE equalizer can be improved by utilizing interference suppression. Simulation results for a GSM system under realistic conditions are presented.

Pan-European speech coding standard for digital mobile radio

This paper considers the application of constant-amplitude, partial-response, continuous-phase modulation with simple near-optimum receivers to cellular digital mobile radio systems. These smoothed modulation schemes have low spectral sidelobes and narrow main lobes. A combiner for time-division retransmission systems with space diversity is given for continuous-phase modulation. Cochannel interference and adjacent-channel interference are calculated for continuous-phase modulation in cellular systems with frequency reuse. The efficiency of 3RC and 4RC modulations with space diversity is evaluated for conventional cellular systems.

The authors study an adaptive decision feedback equalizer (DFE) for application in the USA digital cellular radio telephone system. A synchronous DFE and a fractionally spaced DFE are adaptive and use a fast recursive least squares algorithm to track rapid channel variations. Simulation results indicating the performance sensitivity to time delay spread, Doppler shift, and timing jitter are presented. A DFE using a complex fast-Kalman adaptation algorithm is presented, and its bit error rate performance evaluated. The fast Kalman equalizer is found to possess good tracking ability and can track channel variations at vehicle speeds of 50 mph (80 km/h). Sensitivity to sample timing jitter can be reduced by using a DFE with fractionally spaced feedforward taps. >

Pilot-symbol aided coherent M-ary PSK modems in digital cellular mobile radio systems are analyzed theoretically. The error-floors caused by the Doppler spread in a fast fading channel are removed in both flat and selective fading channels. However, the error-floors caused by the delay spread are lower-bounded by those that exist in the ideal coherent detection. The systems are modeled as frequency-selective fast Rayleigh fading channels, corrupted by co-channel interference (CCI) and additive white Gaussian noise (AWGN). In the proposed scheme, pilot symbols are inserted periodically to monitor the channel characteristics. The fading processes experienced by the pilot symbols are used to estimate those suffered by the data symbols using interpolation or filtering. The estimated fade characteristics are used to compensate the random phase variation caused by the Doppler spread, so that the signals can be demodulated coherently. The theoretical performances of the fade compensated coherent modems are evaluated. The results show that the fade compensated coherent demodulation with the least redundancy achieves the same performance as the ideal differential detection in a fading channel. The performance approaches that of the ideal coherent demodulation as more redundancy is allowed. The pilot-symbol-insertion (PSI) scheme is also applicable to M-ary QAM modems and Rician channels. The residual frequency offset can also be compensated by the PSI technique.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>