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Convolutional codes with optimum distance spectrum

New convolutional codes with rates 1/2, 1/3, and 1/4 are presented for constraint lengths ranging from 3 to 15. These new codes are maximum free-distance codes. Furthermore, the codes have optimized information error weights, resulting in a low bit-error rate for binary communication on both additive white Gaussian noise (AWGN) and Rayleigh fading channels. Improved coding gains of as much as 0.6 dB compared to previously published codes have been observed for coherent BPSK over a Rayleigh fading channel and a wide range of signal-to-noise ratios.

Design of Optimal High-Rank Line-of-Sight MIMO Channels

This paper describes a technique for realizing a high-rank channel matrix in a line-of-sight (LOS) multiple-input multiple-output (MIMO) transmission scenario. This is beneficial for systems which are unable to make use of the originally derived MIMO gain given by independent and identically distributed (i.i.d.) flat Rayleigh fading subchannels. The technique is based on optimization of antenna placement in uniform linear arrays with respect to mutual information (MI). By introducing a new and more general 3-D geometrical model than that applied in earlier work, additional insight into the optimal design parameters is gained. We also perform a novel analysis of the sensitivity of the optimal design parameters, and derive analytical expressions for the eigenvalues of the pure LOS channel matrix which are valid also when allowing for non-optimal design. Furthermore, we investigate the approximations introduced in the derivations, in order to reveal when the results are applicable. The LOS matrix is employed in a Ricean fading channel model, and performance is evaluated with respect to the average MI and the MI cumulative distribution function. Our results show that even with some deviation from the optimal design, the LOS MEMO case outperforms the i.i.d. Rayleigh case in terms of MI.

Code-spread CDMA using maximum free distance low-rate convolutional codes

In code division multiple-access (CDMA) systems, maximum total throughput assuming a matched filter receiver can be obtained by spreading with low-rate error control codes. Previously, orthogonal, bi-orthogonal and super-orthogonal codes have been proposed for this purpose. We present in this paper a family of rate-compatible low-rate convolutional codes with maximum free distance. The performance of these codes for spectrum spreading in a CDMA system is evaluated and shown to outperform that of orthogonal and super-orthogonal codes as well as conventionally coded and spread systems. We also show that the proposed low rate codes will give simple encoder and decoder implementations. With these codes, any rate 1/n, n/spl les/512, are obtained for constraint lengths up to 11, resulting in a more flexible and powerful scheme than those previously proposed.

Construction and capacity analysis of high-rank line-of-sight MIMO channels

This paper describes a technique for realizing a high rank channel matrix in a line-of-sight (LOS) multiple-input-multiple-output (MIMO) transmission scenario. This is beneficial for systems which can not make use of the originally derived MIMO gain given by independent and identically distributed (i.i.d.) flat Rayleigh fading channels. Typical applications are fixed wireless access and radio relay systems. The technique is based on optimization of antenna placement in a uniform linear array. By introducing a new and more general geometrical model than that applied in earlier works, additional insight into the optimal design parameters is gained. A novel analysis of the sensitivity of the optimal design parameters is performed. The LOS transmission matrix is used in a Rician fading channel model, and performance is evaluated with respect to ergodic capacity, outage capacity, and effective degrees of freedom. The results show that even with some deviation from optimal design, the LOS MIMO case outperforms the i.i.d. Rayleigh case in terms of Shannon capacity.

Rate-compatible convolutional codes for multirate DS-CDMA systems

New rate-compatible convolutional (RCC) codes with high constraint lengths and a wide range of code rates are presented. These new codes originate from rate 1/4 optimum distance spectrum (ODS) convolutional parent encoders with constraint lengths 7-10. Low rate encoders (rates 115 down to 1/10) are found by a nested search, and high rate encoders (rates above 1/4) are found by rate-compatible puncturing. The new codes form rate-compatible code families more powerful and flexible than those previously presented. It is shown that these codes are almost as good as the existing optimum convolutional codes of the same fates. The effects of varying the design parameters of the rate-compatible punctured convolutional (RCPC) codes, i.e., the parent encoder rate, the puncturing period, and the constraint length, are also examined. The new codes are then applied to a multicode direct-sequence code-division multiple-access (DS-CDMA) system and are shown to provide good performance and rate-matching capabilities. The results, which are evaluated in terms of the efficiency for Gaussian and Rayleigh fading channels, show that the system efficiency increases with decreasing code rate.

Code-spread CDMA with interference cancellation

The performance of an asynchronous code division multiple access (CDMA) system (uplink) employing very low-rate maximum free distance codes for combined coding and spreading is analyzed when successive or parallel interference cancellation is applied. An analytical approach to the evaluation of the bit error rate is presented and shown to give results close to simulations. Our results show that the code-spread system outperforms the conventionally coded and spread system. Without interference cancellation the single-user bound is never reached (except for one user). With two stages of parallel interference cancellation, a code-spread system with a load only slightly less than 1 bit/chip can obtain a bit error rate very close to that of a single-user system.

Optimal Discrete-Level Power Control for Adaptive Coded Modulation Schemes with Capacity-Approaching Component Codes

In wireless communications, bandwidth is a scarce resource. By employing link adaptation we achieve bandwidth-efficient wireless transmission schemes. Using a fixed number of codes we propose a variable-power transmission scheme for slowly flat-fading channels. Assuming that capacity-achieving codes for AWGN channels are available, we develop new combined discrete-rate discrete-power adaptation algorithms with limited feedback for wireless systems. The adaptation schemes are optimized in order to maximize the average spectral efficiency (ASE) for any finite number of available rates. We show that the new transmission schemes can achieve significantly higher ASE when compared to constant power schemes, almost reaching the upper bound of continuous power adaptation. Specifically, using just four rates and four power levels per rate results in a spectral efficiency that is within 1 dB of the continuous-rate continuous-power Shannon capacity. Further, the novel discrete transmission schemes reduce the probability of outage and are more robust against imperfect channel estimation and prediction.

Adaptive Multi-Channel Transmission Power Control for Industrial Wireless Instrumentation

The adoption of wireless technology for industrial wireless instrumentation requires high-quality communication performance. The use of transmission power control (TPC) can help address industrial issues concerning energy consumption, interference, and fading. This paper presents a TPC algorithm designed for industrial applications based on theoretical and empirical studies. It is shown that the proposed algorithm adapts to variations in link quality, and is hardware-independent and practical.

Rate matching in multichannel systems using RCPC-codes

Rate-compatible punctured convolutional codes (RCPC-codes) are proposed for rate matching in multichannel multiple access systems. The bit error rate performance of a multicode direct-sequence code-division multiple-access (DS-CDMA) based system using RCPC-codes is used to evaluate the proposed rate matching scheme. Comparison with repetition encoding is also made. The RCPC-codes outperforms the repetition codes and can provide a larger span of available channel coding rates. We show that RCPC-codes provide a flexible coding scheme suitable for future mobile radio communication systems.

Optimal Design of Uniform Planar Antenna Arrays for Strong Line-of-Sight MIMO Channels

We investigate the optimal design of uniform planar antenna arrays employed in multiple-input multiple-output communications where a strong line-of-sight (LOS) component is present. A new general geometrical model is introduced to model the LOS channel, which allows for any orientation of the two arrays. Based on this model, we derive the optimal design equations with respect to maximizing Shannon capacity, which turn out to be solvable for several interesting cases. The solutions reveal that the proposed principle is best suited for fixed applications, as e.g. fixed wireless access. The LOS channel matrix is used in a Ricean channel model to evaluate performance under different channel conditions. Results show that even with some deviation from the optimal design, we get good performance compared to the case of uncorrelated Rayleigh subchannels