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In this paper, we first derive the theoretical performance of a complementary code keying (CCK) code on an additive white Gaussian noise (AWGN) channel and over a multipath channel. To derive the error performance, we use the weight and cross-correlation distributions of the CCK code for optimal and suboptimal decoding, respectively, based on union bound. In addition, we propose a RAKE receiver for a CCK modem, which is suitable for a multipath environment with a large delay spread. The RAKE receiver principle is acceptable for modest multipath because it can coherently combine multipath components to provide signal-to-noise ratio (SNR) enhancement. However, as the delay spread is larger and the data rate of systems goes higher, intersymbol interference (ISI) generated due to multipath environments are increased. To handle the increasing ISI, the CCK modem needs an equalization technique to remove the ISI, together with RAKE processing. Thus, our proposed system is based on a channel matched filter (CMF) with a decision feedback equalizer (DFE). The CMF is applied for RAKE processing, whereas the DFE structure is used for ISI cancellation. In our system, ISI is calculated and removed by using a decoded CCK codeword. Index Terms--Complementary code keying (CCK), decision feedback equalizer (DFE), equalization, RAKE receiver.

This paper introduces a novel approach to data communication over the Global System for Mobile Communications (GSM) voice channel. It is based on the concept of 'symbols'--a set of predefined signals with finite bandwidths. Data are encoded into the symbols, and the symbols are voice coded as they were speech, modulated into the GSM signal, sent over the air, GSM demodulated, voice decoded, and converted back to data. The symbols are synthesized by a genetic algorithm with the aim of maintaining separability after passing them through the voice codec. This method enables data transfer over communication networks that do not have dedicated data channels and could also be used in conjunction with other data services to balance the system load between data and voice channels, allowing optimization of system resources. We present the full algorithmic structure of the system, which performs data communications over the GSM voice channel, and we also give the results of the performance tests. Index Terms--Data communications, genetic algorithms (GAs), mobile communications, vocoders.

In an all-digital timing-adjustment system for digital modems, interpolation can be employed to recover samples that are synchronous with the data symbols. In this paper, a novel interpolation method is described for such systems. Instead of approximating a continuous-time signal with a conventional (algebraic) polynomial and computing the synchronized samples using a Farrow structure, a trigonometric polynomial is employed. It is demonstrated that this approach produces a particularly simple implementation structure, reduces computational delay and, for practical signals, can improve the interpolation performance. Moreover, to recover a synchronized sample from existing samples, given a timing offset, it is shown that the method can be optimized such that a recovered sample's interpolation error is minimized for that specific timing offset value. The input signal's spectrum is also taken into account. Simulation results indicate that the method can achieve the best performance among all state-of-the-art methods tested. In addition, the optimal interpolator can be implemented without increased hardware requirements. Index Terms--Fractional delay filter, interpolation, sample-rate conversion, synchronization, timing recovery, trigonometric polynomial.

Modems designed for the public switched telephone network (PSTN) have conventionally been based on modeling assumptions which view the PSTN connection as an essentially analog medium. However, as the PSTN evolves toward all digital transport and switching, and particularly as major traffic sources, such as Internet service providers, increasingly have direct digital connections to the PSTN, it is appropriate to revisit the model assumptions. Recently, several modem and chipset manufacturers have announced "56K" modems based on an emerging system paradigm in which one user (a residential Internet subscriber) has an analog connection to the PSTN, and the other (an Internet service provider) has a digital one. ITU-T is expected to finalize details of a corresponding recommendation in 1998. With this configuration, modem designs based on signaling with the [Mu]law alphabet become feasible, and the conventional Shannon limit disappears as the quantization noise is avoided. Thus, the conventional Shannon limit of about 36 kb/s can be beaten, and it is possible to approach the digital transmission rate of 64 kb/s. Modems employing this general approach have become known as [Mu]-law or pulse-code modulation (PCM) modems. In this paper we present a signaling technique and the sampling theory based on this technique, display the structure and operating principles of a PCM modem equalizer, and show how this equalizer problem can be cast in the language of multi-input-multi-output (MIMO) system theory. Index Terms - 56K modem, equalization, multi-input-multi-output (MIMO) systems, nonuniform sampling, Nyquist bandwidth limit, PCM modem, Shannon capacity limit, V.90.

A study was conducted on the incorporation of environmental issues in the design cycle of telecommunications products such as the asymmetric digital subscriber loop high speed modem. The green design methodology emphasized life cycle assessment (LCA) as well as design for environment (DFE). A case study involving the LCA implementation into a specific DFE approach shows that environmental design concerns may be considered as one of the many design constraints.

This paper deals with the key synchronization aspects in the system design of a QQPSK (quadrature - quadrature phase shift-keying) modem. We discuss the sensitivity of the data demodulator to synchronization errors and contextually we evaluate both theoretically and by computer simulations the performance of some IF and baseband carrier phase and symbol timing recovery schemes. In particular, we take into consideration a fourth-power IF carrier/clock regenerator and two baseband clock recovery schemes, with and without the aid of data decisions, respectively. The analysis shows on one side the substantial robustness of QQPSK to carrier phase errors and the adequacy of the examined carrier extraction scheme. On the other hand, the remarkable sensitivity of QQPSK to symbol timing inaccuracy is stressed and the need to resort to the newly proposed decision-aided baseband clock recovery scheme is pointed out.

This letter presents the method useful in subscriber line qualification for asymmetric digital subscriber line service. It is based on the results of the line frequency response measurement in the voice band by V.34 modems. The response is related to the line attenuation at 300 kHz. The measurement results are also presented. Index Terms--Access networks, asymmetric digital subscriber line (ADSL), attenuation, broadband services, data transmission, line qualification, subscriber loop, V.34.