Channel Estimation And Multiuser Detection In Asynchronous Satellite Communications

In this paper, we propose a new method of channel estimation for asynchronous additive white Gaussian noise channels in satellite communications. This method is based on signals correlation and multiuser interference cancellation which adopts a successive structure. Propagation delays and signals amplitudes are jointly estimated in order to be used for data detection at the receiver. As, a multiuser detector, a single stage successive interference cancellation (SIC) architecture is analyzed and integrated to the channel estimation technique and the whole system is evaluated. The satellite access method adopted is the direct sequence code division multiple access (DS CDMA) one. To evaluate the channel estimation and the detection technique, we have simulated a satellite uplink with an asynchronous multiuser access.Comment: 14 pages, 9 figure

Successive AF/DF Relaying in the Cooperative DS-CDMA Uplink: Capacity Analysis and its System Architecture

A successive relaying aided network (SRAN) is designed for a multi-user spread-spectrum scenario conceived for noncoherent (NC) detection in order to convert the typical 50% half-duplex relaying-induced throughput loss to a potential user-load reduction of the CDMA system, where the NC allows us to avoid the extra power consumption imposed by channel estimation. We commence by evaluating the noncoherent Discrete-input Continuous-output Memoryless Channel (DCMC) capacity of both the Amplify-and-Forward (AF) based and of the Decode-and-Forward (DF) based SRAN in the DS-CDMA uplink. Whilst NC detection has the added benefit of eliminating both the pilot-overhead and power-hungry channel estimation, it tends to form an error-floor at high Doppler frequencies. We mitigate this problem using multiple-symbol detection, which increases the detection complexity upon extending the detection window. Finally, a relay-aided soft-input soft-output Multiple-Symbol Differential Sphere Detection (SISO-MSDSD) CDMA regime is proposed, which significantly reduces the system’s complexity without sacrificing its performance

Uplink channel estimation for IMT-DS system

The IMT-DS system is one of the approved 3G radio interface standards which employ RAKE receivers to exploit multipath diversity. This paper discusses a new dimension in DS-CDMA channel estimation, i.e., chip-level adaptive channel estimation. A novel despreader-respreader based channel estimator (DRCE) is proposed to obtain uplink (UL) channel estimates at chip-level which resolves the deficiencies of conventional methods that work at symbol level. The DRCE employs an adaptive filter whose weights are adapted by using an LMS algorithm. The performance of the RAKE receiver with DRCE for an IMT-DS system is evaluated in terms of BER by simulations for pedestrian and vehicular channel

Uplink channel estimation for IMT-DS system

The IMT-DS system is one of the approved 3G radio interface standards which employ RAKE receivers to exploit multipath diversity. This paper discusses a new dimension in DS-CDMA channel estimation, i.e., chip-level adaptive channel estimation. A novel despreader-respreader based channel estimator (DRCE) is proposed to obtain uplink (UL) channel estimates at chip-level which resolves the deficiencies of conventional methods that work at symbol level. The DRCE employs an adaptive filter whose weights are adapted by using an LMS algorithm. The performance of the RAKE receiver with DRCE for an IMT-DS system is evaluated in terms of BER by simulations for pedestrian and vehicular channel

ISMA-DS/CDMA MAC protocol for mobile packet radio networks

In this paper an ISMA-DS/CDMA MAC protocol for a packet transmission network is presented. The main feature of this protocol is its ability to retain the inherent flexibility of random access protocols while at the same time reducing to some extent the randomness in the access in order to increase the system capacity. In this framework, the protocol is adapted to a frame structure similar to that specified in the UTRA ETSI proposal for third generation mobile communication systems. Additionally, some adaptive mechanisms are proposed that improve protocol performance by means of varying the transmission bit rate according to the channel load that is broadcast by the base station. As a result, an adaptive bit rate algorithm is presented that reaches a throughput value close to the optimumPeer ReviewedPostprint (published version

Fixed-complexity quantum-assisted multi-user detection for CDMA and SDMA

In a system supporting numerous users the complexity of the optimal Maximum Likelihood Multi-User Detector (ML MUD) becomes excessive. Based on the superimposed constellations of K users, the ML MUD outputs the specific multilevel K-user symbol that minimizes the Euclidean distance with respect to the faded and noise-contaminated received multi-level symbol. Explicitly, the Euclidean distance is considered as the Cost Function (CF). In a system supporting K users employing M-ary modulation, the ML MUD uses MK CF evaluations (CFE) per time slot. In this contribution we propose an Early Stopping-aided Durr-Høyer algorithm-based Quantum-assisted MUD (ES-DHA QMUD) based on two techniques for achieving optimal ML detection at a low complexity. Our solution is also capable of flexibly adjusting the QMUD's performance and complexity trade-off, depending on the computing power available at the base station. We conclude by proposing a general design methodology for the ES-DHA QMUD in the context of both CDMA and SDMA systems