Minimum cell size for information capacity increase in cellular wireless network

In conventional cellular wireless communication system, interference modelling has focused on the six primary co-channel interfering cells (first tier co-channel cells). In the current accepted interference model, co-channel interfering cells beyond the first tier (subsequent tier co-channel cells) are neglected. This currently accepted interference models is suitable for cellular wireless communication systems operating at carrier frequencies, f c = 0.9 and 1.8 GHz, cell size radii R > 1 km and basic path loss exponent α ≥ 2. The future and emerging wireless communication systems are expected to be operating at frequencies f c > 2 GHz (3.35 - 15.75 GHz), cell size radii R≤ 1 km and basic path loss exponent α ≤ 2. This, makes the current acceptable co-channel interference model unsuitable for information capacity analysis of the future cellular systems. Therefore, a co-channel interference model suitable for future and emerging wireless communication system becomes necessary. In this thesis a new and modified interference model is proposed. The proposed interference model includes the first and subsequent tier co-channel interfering cells. The proposed interference model will be suitable for cellular wireless communication systems operating at carrier frequencies f c > 2 GHz, cell size radii R≤ 1 km and basic path loss exponent α ≤ 2. A mathematical analysis, supported by computer simulation is used, to study the uplink information capacity performance for the conventional and proposed interference model. The analysis and simulation results of the proposed interference model show that at carrier frequencies f c > 2 GHz, co-channel interfering cells beyond the first tier become active as cell size radius R, reduces. As an example for a carrier frequency f c = 15.75 GHz, cell size radius R = 100 m at a normalized reuse distance Ru = 4, there was a 15.32 % decrease in the information capacity between the conventional and proposed interference model. An information capacity - cost analysis is used to find a minimum cell size for information capacity increase in cellular wireless network, thus a theoretical limit to cell size reduction. The results show that as the cell size radius R reduces to 300 m and less, the proposed interference model show a 5.76 - 18.89 % decrease in the information capacity per unit cost (£, $, etc) at microwave carrier frequencies f c > 3.35 GHz. This result illustrates that there is a theoretical limit to cell size reduction in relation to information capacity performance and cost. An inductive approach is used to generate a formula for calculating the number of co-channel interfering cells Nn in a cellular wireless site layout. Such a formula allows one to calculate the number of co-channel interfering cells in subsequent tiers of a cellular wireless site layout. The geometric derivation shows that the number of co-channel interfering cell Nn in a subsequent tier is the product of the number of co-channel interfering cells in the first tier NI and the tier number n. Thus, the number of co-channel interfering cell in a subsequent tier Nn = NI × n. This formula enables subsequent tier co-channel interference to be included in the information capacity analysis of future and emerging, and finding the minimum cell size for information capacity increase in a cellular wireless communication system

Pilot Decontamination in CMT-based Massive MIMO Networks

Pilot contamination problem in massive MIMO networks operating in time-division duplex (TDD) mode can limit their expected capacity to a great extent. This paper addresses this problem in cosine modulated multitone (CMT) based massive MIMO networks; taking advantage of their so-called blind equalization property. We extend and apply the blind equalization technique from single antenna case to multi-cellular massive MIMO systems and show that it can remove the channel estimation errors (due to pilot contamination effect) without any need for cooperation between different cells or transmission of additional training information. Our numerical results advocate the efficacy of the proposed blind technique in improving the channel estimation accuracy and removal of the residual channel estimation errors caused by the users of the other cells.Comment: Accepted in ISWCS 201

Performance limits for channelized cellular telephone systems

Studies the performance of channel assignment algorithms for “channelized” (e.g., FDMA or TDMA) cellular telephone systems, via mathematical models, each of which is characterized by a pair (H,p), where H is a hypergraph describing the channel reuse restrictions, and p is a probability vector describing the variation of traffic intensity from cell to cell. For a given channel assignment algorithm, the authors define T(r) to be the amount of carried traffic, as a function of the offered traffic, where both r and T(r) are measured in Erlangs per channel. They show that for a given H and p, there exists a function TH,p(r), which can be computed by linear programming, such that for every channel assignment algorithm, T(r) ≤ TH,p(r). Moreover, they show that there exist channel assignment algorithms whose performance approaches TH,p (r) arbitrarily closely as the number of channels increases. As a corollary, they show that for a given (H,p) there is a number r0 , which also can be computed by linear programming, such that if the offered traffic exceeds r0, then for any channel assignment algorithm, a positive fraction of all call requests must be blocked, whereas if the offered traffic is less than r0, all call requests can be honored, if the number of channels is sufficiently large. The authors call r0, whose units are Erlangs per channel, the capacity of the cellular system

Frequency planning for clustered jointly processed cellular multiple access channel

Owing to limited resources, it is hard to guarantee minimum service levels to all users in conventional cellular systems. Although global cooperation of access points (APs) is considered promising, practical means of enhancing efficiency of cellular systems is by considering distributed or clustered jointly processed APs. The authors present a novel `quality of service (QoS) balancing scheme' to maximise sum rate as well as achieve cell-based fairness for clustered jointly processed cellular multiple access channel (referred to as CC-CMAC). Closed-form cell level QoS balancing function is derived. Maximisation of this function is proved as an NP hard problem. Hence, using power-frequency granularity, a modified genetic algorithm (GA) is proposed. For inter site distance (ISD) <; 500 m, results show that with no fairness considered, the upper bound of the capacity region is achievable. Applying hard fairness restraints on users transmitting in moderately dense AP system, 20% reduction in sum rate contribution increases fairness by upto 10%. The flexible QoS can be applied on a GA-based centralised dynamic frequency planner architecture

System-Level Modelling and Beamforming Design for RIS-assisted Cellular Systems

Reconfigurable intelligent surface (RIS) is considered as key technology for improving the coverage and network capacity of the next-generation cellular systems. By changing the phase shifters at RIS, the effective channel between the base station and user can be reconfigured to enhance the network capacity and coverage. However, the selection of phase shifters at RIS has a significant impact on the achievable gains. In this letter, we propose a beamforming design for the RIS-assisted cellular systems. We then present in detail the system-level modelling and formulate a 3-dimension channel model between the base station, RIS, and user, to carry out system-level evaluations. We evaluate the proposed beamforming design in the presence of ideal and discrete phase shifters at RIS and show that the proposed design achieves significant improvements as compared to the state-of-the-art algorithms

Hypergraph Models for Cellular Mobile Communication Systems

Cellular systems have hitherto been modeled mostly by graphs for the purpose of channel assignment. However, hypergraph modeling of cellular systems offers a significant advantage over graph modeling in terms of the total traffic carried by the system. For example, we show that a 37-cell system when modeled by a hypergraph carries around 30% more traffic than when modeled by a graph. We study the performance of channelized cellular systems modeled by hypergraphs in comparison with those modeled by graphs. For this purpose, we have evaluated the capacities of these cellular networks defined [3]. Evaluation of the capacity necessitates generation of maximal independent sets of hypergraphs. We describe some new algorithms that we have developed for this purpose

Impact of inter-cell interference on capacity in the joint multiple access (CDMA and SDMA) system

Spatial filtering using smart antenna has emerged as a promising technique to improve the performance of cellular systems. Cell splitting and sectorisation in CDMA systems could result in an increase in system capacity. In this paper, we investigate the impact of inter-cell interference on reverse link capacity in a joint multiple access system arising from the combination of CDMA and SDMA systems. The system capacity of CDMA and SDMA systems is reviewed individually. The co-channel and antenna side-lobes interferences in SDMA systems due to the randomly located mobile users in a non-uniform traffic cell are studied. Therefore, the most realistic reverse link capacity improvement of the joint multiple access system is presented here by taking into consideration both intra-sector and inter-sector interferences. The results are based on the system parameters of CDMA and SDMA systems