4,569 research outputs found
Accurate BER Analysis of QPSK Modulated Asynchronous DS-CDMA Systems Communicating over Rayleigh Channels
The accurate average BER calculation of an asynchronous DS-CDMA system using random spreading sequences is studied in Rayleigh fading channels. An accurate closed-form expression is derived for the conditional characteristic function of the multiple access interference. An accurate BER expression is provided, which only requires a single numerical integration. Our numerical simulation results verify its accuracy, and also demonstrate the relative inaccuracy of the Gaussian approximation
Exact BER Performance of Asynchronous DS-CDMA Systems using Quadriphase Spreading and QPSK Modulation over Rayleigh Channels
An accurate closed-form expression is derived for calculating the average BER in an asynchronous DS-CDMA system using random complex-valued spreading sequences for transmission over Rayleigh channels. This accurate solution is based on the Characteristic Function (CF) approach and only requires a single numerical integration. Our numerical simulation results verify its accuracy, and also demonstrate the relative inaccuracy of the Gaussian approximation
Exact BER Calculation of Asynchronous DS-CDMA Systems Communicating over Hoyt Channels
An asynchronous binary DS-CDMA system using random spreading sequences is considered in flat Hoyt fading channels. A new closed-form expression is derived for the conditional characteristic function of the multiple access interference. The exact average BER is expressed as a single numerical integration based on the characteristic function approach. The numerical results obtained from our exact BER analysis are verified by our simulation results and also compared to those obtained by the standard Gaussian approximation
Precise BER Formulas for Asynchronous QPSK-Modulated DS-CDMA Systems Using Random Quaternary Spreading Over Rayleigh Channels
Precise bit-error-ratio (BER) analysis of an asynchronous QPSK-modulated direct-sequence code-division multiple-access system using random quaternary spreading sequences for transmission over Rayleigh channels is performed based on the characteristic-function approach. Its accuracy is verified by our numerical simulation results and also compared with those of the Gaussian approximation. Index Terms—Asynchronous direct-sequence code-division multiple-access (DS-CDMA), bit-error-ratio (BER), precise, QPSK, quarternary spreading, Rayleigh
A Unified Exact BER Performance Analysis of Asynchronous DS-CDMA Systems Using BPSK Modulation over Fading Channels
Abstract—An asynchronous binary DS-CDMA system using random spreading sequences is considered when communicating over various fading channels. New closed-form expressions are derived for the conditional Characteristic Function (CF) of the multiple access interference. A unified analysis is provided for calculating the exact average Bit Error Rate (BER) expressed in the form of a single numerical integration based on the CF approach. The numerical results obtained from our exact BER analysis are verified by our simulation results and are also compared to those obtained by the Standard Gaussian Approximation (SGA), confirming the accuracy of the SGA for most practical conditions, except for high Signal-to-Noise Ratios (SNR) and for a low number of interferers. Index Terms—BER analysis, CDMA, fading, Rayleigh, Ricean, Hoyt, Nakagami-m, random spreading sequence
Analytical BER Performance of DS-CDMA Ad Hoc Networks using Large Area Synchronized Spreading Codes
The family of operational CDMA systems is interference-limited owing to the Inter Symbol Interference (ISI) and the Multiple Access Interference (MAI) encountered. They are interference-limited, because the orthogonality of the spreading codes is typically destroyed by the frequency-selective fading channel and hence complex multiuser detectors have to be used for mitigating these impairments. By contrast, the family of Large Area Synchronous (LAS) codes exhibits an Interference Free Window (IFW), which renders them attractive for employment in cost-efficient quasi-synchronous ad hoc networks dispensing with power control. In this contribution we investigate the performance of LAS DS-CDMA assisted ad hoc networks in the context of a simple infinite mesh of rectilinear node topology and benchmark it against classic DS-CDMA using both random spreading sequences as well as Walsh-Hadamard and Orthogonal Gold codes. It is demonstrated that LAS DS-CDMA exhibits a significantly better performance than the family of classic DS-CDMA systems operating in a quasi-synchronous scenario associated with a high node density, a low number of resolvable paths and a sufficiently high number of RAKE receiver branches
Analytical Bit Error Rate Performance of DS-CDMA Ad Hoc Networks using Large Area Synchronous Spreading Sequences
The performance of large area synchronous (LAS) direct sequence code division multiple access (DS-CDMA) assisted ad hoc networks is investigated in the context of a single-hop infinite mesh of rectilinearly located ad hoc nodes. It is shown that LAS DS-CDMA exhibits a significantly better performance than the family of traditional spreading sequences used in a quasisynchronous DS-CDMA scenario having a low number of resolvable multipath components and a sufficiently high number of RAKE receiver branches. The benefits of LAS codes in ad hoc networks are multifold: (i) Their performance is noise-limited, rather than interference-limited, provided that the multipath and multi-user interference arrives within their interference free window. (ii) Under the same conditions LAS codes are robust against the ‘near–far’ effects imposed by ad hoc networks operating without base-station-aided power control, without accurate synchronisation and without implementationally complex interference cancellers
Analytical Studies of Fragmented-Spectrum Multi-Level OFDM-CDMA Technique in Cognitive Radio Networks
In this paper, we present a multi-user resource allocation framework using
fragmented-spectrum synchronous OFDM-CDMA modulation over a frequency-selective
fading channel. In particular, given pre-existing communications in the
spectrum where the system is operating, a channel sensing and estimation method
is used to obtain information of subcarrier availability. Given this
information, some real-valued multi-level orthogonal codes, which are
orthogonal codes with values of , are provided
for emerging new users, i.e., cognitive radio users. Additionally, we have
obtained a closed form expression for bit error rate of cognitive radio
receivers in terms of detection probability of primary users, CR users' sensing
time and CR users' signal to noise ratio. Moreover, simulation results obtained
in this paper indicate the precision with which the analytical results have
been obtained in modeling the aforementioned system.Comment: 6 pages and 3 figure
Performance Evaluation of Impulse Radio UWB Systems with Pulse-Based Polarity Randomization
In this paper, the performance of a binary phase shift keyed random
time-hopping impulse radio system with pulse-based polarity randomization is
analyzed. Transmission over frequency-selective channels is considered and the
effects of inter-frame interference and multiple access interference on the
performance of a generic Rake receiver are investigated for both synchronous
and asynchronous systems. Closed form (approximate) expressions for the
probability of error that are valid for various Rake combining schemes are
derived. The asynchronous system is modelled as a chip-synchronous system with
uniformly distributed timing jitter for the transmitted pulses of interfering
users. This model allows the analytical technique developed for the synchronous
case to be extended to the asynchronous case. An approximate closed-form
expression for the probability of bit error, expressed in terms of the
autocorrelation function of the transmitted pulse, is derived for the
asynchronous case. Then, transmission over an additive white Gaussian noise
channel is studied as a special case, and the effects of multiple-access
interference is investigated for both synchronous and asynchronous systems. The
analysis shows that the chip-synchronous assumption can result in
over-estimating the error probability, and the degree of over-estimation mainly
depends on the autocorrelation function of the ultra-wideband pulse and the
signal-to-interference-plus-noise-ratio of the system. Simulations studies
support the approximate analysis.Comment: To appear in the IEEE Transactions on Signal Processin
Exact BER Performance of Asynchronous MC-DS-CDMA over Fading Channels
In this contribution an accurate average Bit Error Rate (BER) formula is derived for MC-DS-CDMA in the context of asynchronous transmissions and random spreading sequences. We consider a flat Nakagami-m fading channel for each subcarrier. Our analysis is based on the Characteristic Function (CF) and does not rely on any assumption concerning the statistical behavior of the interference. We develop a new closed-form expression for the conditional CF of the inter-carrier interference and provide a procedure for calculating the exact BER expressed in the form of a single numerical integration. The accuracy of the Standard Gaussian Approximation (SGA) technique is also evaluated. Link-level results confirm the accuracy of the SGA for most practical conditions
- …