Bogdan Timus

Cost analysis issues in a wireless multihop architecture with fixed relays

The infrastructure costs of a hybrid cellular-multihop and a traditional single-hop cellular system are compared in this paper with the help of a linear cost model. The cost is evaluated in a greenfield operator scenario most suited in a suburban type of environment, by defining a desired service level as achieved bit-rate per area unit [kbps/km/sup 2/]. The hybrid system consists of macro base stations and fixed wireless routers. The impact of the radio resource allocation scheme on the cost is exemplified with schemes: a cell-based TDMA scheme and a centralized STDMA scheme. Numerical results show that the hybrid system outperforms the traditional one in terms of infrastructure cost if the STDMA scheme is used and if the cost of a relay is 3 to 7% of the macro base station cost, depending on the desired service level.

Uplink admission control for conversational services using information from many cells

The 3G cellular mobile systems based on WCDMA technology are expected to be interference limited. In this case, the radio resource availability in a cell will depend on the number and the type of users in both that cell and the surrounding cells. Consequently, heavier traffic may be allowed in a cell without quality degradation, if there is less traffic in the surrounding cells. This paper presents two uplink session admission control algorithms that exploit the natural traffic variation between cells, using a mechanism for exchanging information between cells. The first algorithm is based on an empirical model of the total power received by a base station, while the second is a suboptimal version of the first. Results from simulated scenarios show that user quality can be maintained while unnecessary call blocking is avoided, which can lead to a capacity increase of 10-20% even if a suboptimal approach is taken.

Implications of Fairness Criteria on the Techno-Economic Viability of Relaying Networks

The introduction of relaying techniques into cellular networks is expected to reduce the total infrastructure cost, especially when coverage extension is sought. With the advent of networks such as LTE, guaranteeing high data-rate coverage may become a challenge even for incumbent operators which nowadays provide full coverage for voice service. However it is not straightforward that operators will be able (or want) to guarantee coverage for the high data-rates. In this paper we study how the techno-economic viability of the relaying solution depends on the type of service to be provided by the operator. We exemplify the trade off between coverage and system throughput with two fairness criteria: perfect fairness (coverage guarantee) and proportional fairness. We show that relays provide advantages when the operator is interested in providing bit-rate/QoS guarantees. When maximizing the system throughput or cell capacity, relays are of less value.

Refined Statistical Analysis of Evolution Approaches for Wireless Networks

To meet future traffic and data rate demands, operators have the opportunity to select between a variety of network evolution approaches. This paper presents a new method for evaluating such approaches, in a simple yet operator specific way. The novelty of the method lies in that, with limited complexity, it takes into account not only conventional dimensioning parameters like targeted user experience, average traffic demand, user density and cell sizes, but also three dimensional spatial user and traffic distribution, site specific propagation, and deployment strategies. This is enabled through the use of an explicit city model, capturing the main characteristics of the operators environment. Applying the method to two examples of different cities illustrates the influence of the refinement parameters and their impact on the benefits of two evolution approaches: macro densification and deployment of small cells.

Incremental Deployment with Self-Backhauling Base Stations in Urban Environment

High capacity mobile broadband access requires a dense infrastructure of base stations. The costs associated with the backhaul transmission for these base stations is often a significant part of the total cost of the access network. It has been proposed to use part of the available spectrum to route data between base stations, so-called in-band relaying or self-backhauling. Although self-backhauling may result in a lower total system capacity, we will in this paper show examples where temporary use of in-band relaying postpones investments in fixed backhaul connections. This reduces the total (life-time) cost of the access network. In our incremental strategy example the total cost savings are in the order of 5 to 10%, depending on the relation between the additional equipment cost and the cost of leasing the fixed backhaul. Self-backhauling is not worth implementing when the entire network capacity needs to be achieved up-front, but the savings are significant when service uptake is slow or difficult to predict. The discount rate used in the investment analysis has only a minor impact on the results.

Cross-Layer Resource Allocation Model for Cellular-Relaying Network Performance Evaluation

The enhancement of cellular networks with relaying technologies is expected to bring significant technoeconomic benefits at the expense of more complex resource allocation. Suitable models for solving network dimensioning problems in cellular-relaying networks must handle radio resource allocation among hundreds of links and tackle interactions between networking layers. For this purpose, we propose a novel cross-layer resource allocation model based on average interference and ideal rate adaptation for the physical layer (PHY), time shares for the medium access layer, and fluid flows for the transport and network layers. We formulate a centralized social welfare maximization problem. When the routes are selected with an a priori algorithm, we show that the resource allocation problem admits an equivalent convex formulation. We show a numerical example for how to use the proposed framework for configuring the backhaul link in a practical relaying network. The overall problem of selecting routes and allocating time shares and link rates is nonconvex. We propose an iterative suboptimal algorithm to solve the problem based on a novel approximation of PHY. We state and prove several convergence properties of the algorithm and show that it typically outperforms routing based on signal-to-noise ratio only.

Techno-Economical Viability of Deployment Strategies for Cellular-Relaying Networks

The ability of an operator to respond to changes in demand by incrementally deploying additional network infrastructure is essential. This paper presents a method for evaluating and comparing the economic viability of incremental deployment strategies given a limited initial investment budget. Any strategy is seen as a sequence of deployment decisions. The time-dynamic relation between service quality and demand is taken into account via the limited investment budget (cash flow analysis), while the focus is maintained on the technical properties of the network. As an example, the economic viability of a ID cellular-relaying network is analyzed under greedy deployment strategies. In order for the cellular-relaying solution to be viable, we show that the maximum allowed relay cost decreases with the investment budget.

Evaluation of cell selection algorithms in LTE-Advanced relay networks

The concept of relay has been introduced in LTE-Advanced as a promising approach to enhance network performance. Because of the diversity introduced by deploying relays to a purely macro network, the conventional cell selection schemes do not perform well, leading to noticeable throughput degradation for some of the users. An algorithm attempting to address the issue is the use of data rate mapped from Reference Signal Received Power (RSRP) as the cell selection criterion. This algorithm, however, introduces an extra interference problem. We therefore describe an additional interference avoidance (IA) mechanism to enhance it. Performance evaluation and analysis are carried out to gain insights on the enhanced algorithm and two additional algorithms, both developed in this paper, to demonstrate their effectiveness in improving the throughput. Simulation results show that for relay-enabled networks the new algorithms based on data rates obtained directly from RSRP and the Reference Signal Received Quality (RSRQ) outperform the algorithm based on RSRP with offset. Moreover, the interference issue is well dealt with via the implementation of additional IA.