Wireless LANs (WLANs) offer an alternative to conventional wired LANs in modern organisations that require a flexible network. However, present-day WLANs yield low capacity compared to conventional wired LANs. In a pr...
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Wireless LANs (WLANs) offer an alternative to conventional wired LANs in modern organisations that require a flexible network. However, present-day WLANs yield low capacity compared to conventional wired LANs. In a previous study, we showed that the capacity of a WLAN can be increased by space division multiple access (SDMA). The implementation of a SDMA receiver requires a channel estimation algorithm. Therefore, we compared both a blind and training-based algorithm for channel estimation in an SDMA WLAN. In this paper we present the semi-analytic simulations based on a ray-tracing channel model. For both algorithms we determine (a) the number of symbols needed to obtain a frequency re-use factor of four, (b) compare their robustness and (c) calculate their complexity. As it turns out, the capacity reduction from training can be reduced to a negligible number of symbols (30 in our case study), the training-based algorithm is more robust and the complexity of the blind algorithm exceeds the complexity of the training-based algorithm by one order of magnitude.
This work deals with the asynchronous DS-CDMA reverse link with multiuser detection (MUD) receivers (two stages of parallel interference cancellation) the channel is multipath Rayleigh faded. The trade-off analysis be...
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This work deals with the asynchronous DS-CDMA reverse link with multiuser detection (MUD) receivers (two stages of parallel interference cancellation) the channel is multipath Rayleigh faded. The trade-off analysis between MUD and channel coding is the main topic. A comparison is made between the maximum throughputs (in bits/s/Hz) achievable using multiuser detection and single user detection, for both single cell and cellular systems. The effect of imperfect power control is also investigated. As in a DS-CDMA system a fixed bandwidth expansion can be allocated to either error correction coding or modulation signal spreading this trade-off is also analysed in conjunction with MUD vs. coding. We suppose that BPSK modulation with coherent demodulation is employed.
Coded modulation schemes based on convolutional codes as well as block codes, in particular turbo codes, are considered on AWGN and flat Rayleigh fading channels. It turns out that codes based on Gray mapping are robu...
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Coded modulation schemes based on convolutional codes as well as block codes, in particular turbo codes, are considered on AWGN and flat Rayleigh fading channels. It turns out that codes based on Gray mapping are robust to channel variations, whereas Ungerbock mapping is suitable only if the channel is a-priori known. The most power efficient scheme based on convolutional codes is multilevel coding with parallel decoding. For block codes, however, bit interleaved coded modulation gains by increased codeword length and outperforms the other schemes.
We derive an efficient maximum likelihood soft decision decoding method for peak-to-mean power ratio limiting codes, of interest in OFDM transmission schemes. We extend the well known method of decoding first order Re...
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We derive an efficient maximum likelihood soft decision decoding method for peak-to-mean power ratio limiting codes, of interest in OFDM transmission schemes. We extend the well known method of decoding first order Reed-Muller codes to the case of Q-ary information vectors and Q-PSK modulation. In addition we describe reduced-complexity methods of decoding, which simulations show to lose only fractions of a dB compared to the maximum-likelihood method.
Coded modulation schemes that use a block encoder are known as block coded modulation (BCM) schemes. This paper introduces a new approach, called the structured distance approach, for finding codes to be used with BCM...
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Coded modulation schemes that use a block encoder are known as block coded modulation (BCM) schemes. This paper introduces a new approach, called the structured distance approach, for finding codes to be used with BCM schemes over additive white Gaussian noise (AWGN) channels. A set-theoretic representation of the Euclidean distance between signals of a channel signal constellation is used to find the distance distribution of the code. The code words are obtained from the distance distribution by selecting appropriate signals from the constellation to satisfy the distribution. The proposed approach is specifically suitable for obtaining short general (non-linear) codes with higher rates which result in short soft decoding delays. Codes over arbitrary channel signal constellation with redundancy over space and time are reported.
Much previous work on finding communication systems for the fast Rayleigh fading channel has been based on solutions originally developed for the additive white Gaussian noise channel. In contrast to this, an efficien...
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Much previous work on finding communication systems for the fast Rayleigh fading channel has been based on solutions originally developed for the additive white Gaussian noise channel. In contrast to this, an efficient communication link is here designed and investigated by using the special properties of the time continuous channel as a starting point.
This paper presents design considerations and measurement results of an upconversion modulation loop transmitter IC (PMB 2255) implemented in Siemens 26 GHz Si bipolar technology B6HF. The device consists of a vector ...
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This paper presents design considerations and measurement results of an upconversion modulation loop transmitter IC (PMB 2255) implemented in Siemens 26 GHz Si bipolar technology B6HF. The device consists of a vector modulator, downconversion mixer, a modulation phase-locked loop (PLL) and a three-wire programming bus. Besides power-down and standby modes, added values of switchable filter cutoff frequency and precharge function are also realized for dual- and multi-band digital mobile communication systems such as GSM900, GSM1800 and GSM1900. Based on measurements the device provides an excellent performance in designed intermediate frequency range from 300 to 550 MHz with supply voltage from 2.7 to 4.5 V, ambient temperature from -30 to 85/spl deg/C, and local and RF frequencies up to 2.0 GHz.
We propose a rate adaptive transmission scheme using punctured convolutional codes in a fixed channel reuse strategy with pulse position modulation (PPM) code division multiple access (CDMA) for indoor infrared wirele...
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We propose a rate adaptive transmission scheme using punctured convolutional codes in a fixed channel reuse strategy with pulse position modulation (PPM) code division multiple access (CDMA) for indoor infrared wireless communications. The proposed system varies the code rate of the punctured convolutional codes, that is, the bit rate adaptively depending on the channel conditions, and can achieve the required bit error rate in all space in a cell. We consider nondirected line-of-sight (LOS) downlinks in a channel reuse strategy with hexagonal cells and a reuse factor of three. We show that the proposed system can realize communications in all space in a cell at the expense of bit rate.
This paper presents F-ary convolutional codes for optimal decoding of pulse-amplitude-modulated (PAM) sequences over noisy finite intersymbol interference (ISI) channels. We refer to this new class of codes as 'op...
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This paper presents F-ary convolutional codes for optimal decoding of pulse-amplitude-modulated (PAM) sequences over noisy finite intersymbol interference (ISI) channels. We refer to this new class of codes as 'optimal convolutional codes' (OCCs) for a channel in the sense of maximizing the minimum Euclidean Distance (ED), d/sub min/, between channel output sequences corresponding to distinct input message sequences at the Viterbi detector, super-trellis of convolutional encoder and channel. Due to the mismatch between the base fields of the convolutional encoder and channel, without resorting to analytical methods, an exhaustive computer search algorithm is proposed on a set of convolutional encoders, called 'standard trellis', which have a specific structure in common. This trellis structure offers good properties in finding d/sub min/ of a code associated with a given encoder. This search scheme, as an example, is applied to the 1+4D+D/sup 2/ channel, and search results have shown that the coding gains achieved are comparable to those of the best convolutional codes in a perfect response channel. To overcome the high computational complexity of optimal MLSE decoding, a new simple and efficient reduced state suboptimal decoding algorithm is also suggested.
A scalar quantizer with variable range operating on a sampled first order Markov stationary process is considered. Rate-distortion performance is obtained. Numerical results are presented for the Gauss-Markov inputs.
A scalar quantizer with variable range operating on a sampled first order Markov stationary process is considered. Rate-distortion performance is obtained. Numerical results are presented for the Gauss-Markov inputs.
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