Adaptive Beamforming and Adaptive Modulation-Assisted Network Performance of Multiuser Detection-Aided FDD and TDD CDMA Systems

The network performance of a frequency division duplex and time division duplex (TDD) code division multiple access (CDMA)-based system is investigated using system parameters similar to those of the Universal Mobile Telecommunication System. The new call blocking and call dropping probabilities, the probability of low-quality access, and the required average transmit power are quantified both with and without adaptive antenna arrays (AAAs), as well as when subjected to shadow fading. In some of the scenarios investigated, the system’s user capacity is doubled with the advent of adaptive antennas. The employment of adaptive modulation techniques in conjunction with AAAs resulted in further significant network capacity gains. This is particularly so in the context of TDD CDMA, where the system’s capacity becomes poor without adaptive antennas and adaptive modulation owing to the high base station (BS) to BS interference inflicted as a consequence of potentially using all time slots in both the uplink and downlink of the emerging wireless Internet. Index Terms—Adaptive beamforming, adaptive modulation, code division multiple access (CDMA) systems, Universal Mobile Telecommunication System Terrestrial Radio Access (UTRA), wireless network performance

Dynamic Channel Allocation Techniques Using Adaptive Modulation and Adaptive Antennas

This contribution studies the impact of adaptive quadrature amplitude modulation (AQAM) on network performance when applied to a cellular network, using adaptive antennas in conjunction with both fixed channel allocation (FCA) and locally distributed dynamic channel allocation (DCA) schemes. The performance advantages of using adaptive modulation are investigated in terms of the overall network performance, mean transmitted power, and the average network throughput. Adaptive modulation allowed an extra 51% of users to be supported by an FCA 4-QAM network, while in conjunction with DCA, an additional 54% user capacity was attained. Index Terms—Adaptive antennas, adaptive modulation, adaptive arrays, beam-steering, DCA, dynamic channel allocation

Adaptive Antenna Array Assisted Dynamic Channel Allocation Techniques

Abstract—The performance of base station adaptive antenna arrays (AAAs) is investigated in conjunction with fixed channel allocation (FCA) and dynamic channel allocation (DCA) schemes. Locally distributed DCAarrangements are studied and benchmarked against standard FCA, in the context of both line-of-sight (LOS) and multipath propagation environments. One-, two-, four-, and eight-element AAAs are employed using the sample matrix inversion (SMI) beamforming algorithm, in both the up- and the down-link. In most investigated scenarios, the locally optimized least interference algorithm (LOLIA) exhibited the best overall compromise in terms of a set of combined metrics, such as the forced termination probability, new call blocking probability, and the probability of a low quality access. Index Terms—Adaptive antennas, adaptive array, beamforming, dynamic channel allocation (DCA), network capacity, wireless networks

The Network Performance of Multi-rate FDD-Mode UMTS

The performance of a multi-rate mobile cellular network using the Frequency Division Duplex (FDD) mode of the Code Division Multiple Access (CDMA) based Universal Mobile Telecommunication System (UMTS) is investigated. The new call blocking and call dropping probabilities and the tolerable network load are studied in the context of a multi-rate FDD-mode UMTS network incorporating dynamic threshold assisted soft handovers and shadow fading

Comparative Study of Adaptive Beam-Steering and Adaptive Modulation-Assisted Dynamic Channel Allocation Algorithms

Abstract—A range of dynamic channel allocation (DCA) algorithms, namely, distributed control and locally distributed control assisted DCA arrangements, are studied comparatively. The so-called locally optimized least interference algorithm (LOLIA) emerges as one of the best candidates for future mobile systems, supporting more than twice the number of subscribers in comparison to conventional fixed channel allocation (FCA). It can also cope with unexpected large increases in teletraffic demands while requiring no tedious frequency planning. This is achieved at the cost of more complex call setup and control, and the requirement of fast backbone networks for base station–base station signalling. Adaptive antennas are shown to significantly enhance the capacity of both the LOLIA and FCA-based networks, especially when used in conjunction with adaptive modulation techniques. Index Terms—Adaptive arrays, adaptive modulation, beam steering, dynamic channel allocation (DCA), smart antennas, wireless networking

Recursive least squares semi-blind beamforming for MIMO using decision directed adaptation and constant modulus criterion

A new semi-blind adaptive beamforming scheme is proposed for multi-input multi-output (MIMO) induced and space- division multiple-access based wireless systems that employ high order phase shift keying signaling. A minimum number of training symbols, very close to the number of receiver antenna elements, are used to provide a rough initial least squares estimate of the beamformer0s weight vector. A novel cost function combining the constant modulus criterion with decision-directed adaptation is adopted to adapt the beamformer weight vector. This cost function can be approximated as a quadratic form with a closed-form solution, based on which we then derive the recursive least squares (RLS) semi-blind adaptive beamforming algorithm. This semi-blind adaptive beamforming scheme is capable of converging fast to the minimum mean-square-error beamforming solution, as demonstrated in our simulation study. Our proposed semi-blind RLS beamforming algorithm therefore provides an e±cient detection scheme for the future generation of MIMO aided mobile communication systems