Rainer Schoenen

Capacity and Coverage Analysis of a 3GPP-LTE Multihop Deployment Scenario

Broadband wireless access will be deployed in a cellular way with 3GPP-LTE [1]. For the first rollout the main demand is a huge area coverage. With only few available base station sites that are connected to an access fiber, multihop (relaying) techniques can be used well to fill the coverage gaps. Later with increasing offered traffic, the demand shifts to higher capacity over the area. Even for this purpose relays are beneficial. There is an area around relays where they provide better overall capacity to the user terminal, taking into account all resources used for the first and second hop (the relaying overhead). Relaying or Multihop operation therefore massively improves the coverage as well as the capacity goals at low cost, without the need of a cable or fiber access. This paper analyzes a realistic urban scenario on the island of Jersey. We study the coverage and capacity over the area in three cases. One base station (BS) only, one BS with four relay nodes (RNs), and the latter plus another ring of nine RNs. The BS has fiber access for rates beyond 100 Mbit/s, while the first hop of Relays (HI) is fed over the air from BS using shared resources in the same LTE band. The second hop H2 is fed by the relays of group HI. In this paper we provide the results from numeric analysis based on models we explain here. It is shown that huge gains in coverage and capacity are obtained by relaying.

On PHY and MAC Performance of 3G-LTE in a Multi-Hop Cellular Environment

Next generation cellular radio systems will exceed the limitations of UMTS. The convergence of data and voice traffic will be supported by a flexible OFDM-based PHY layer and an OFDMA-capable MAC layer. The long term evolution (LTE) successor of the 3G systems incorporates this. But problems concerning coverage and capacity at the cell border still remain for the classical cellular layout. Relaying or Multihop operation is an option to massively improve the coverage as well as the capacity issue at low cost, without the need of a cable or fibre access. For the performance analysis of such cellular systems models for ISO-OSI layers 1+2 (PHY+MAC) are needed. In this paper an analytic modelling framework and results are presented for the cellular LTE performance in two multihop scenarios.

HetHetNets: Heterogeneous Traffic Distribution in Heterogeneous Wireless Cellular Networks

A recent approach in modeling and analysis of the supply and demand in heterogeneous wireless cellular networks has been the use of two independent Poisson point processes (PPPs) for the locations of base stations (BSs) and user equipment (UE). This popular approach has two major shortcomings. First, although the PPP model may be a fitting one for the BS locations, it is less adequate for the UE locations mainly due to the fact that the model is not adjustable (tunable) to represent the severity of the heterogeneity (nonuniformity) in the UE locations. Moreover, the independence assumption between the two PPPs does not capture the often-observed correlation between the UE and BS locations. This paper presents a novel heterogeneous spatial traffic modeling that allows statistical adjustment. Simple and nonparameterized, yet sufficiently accurate, measures for capturing the traffic characteristics in space are introduced. Only two statistical parameters related to the UE distribution, namely, the coefficient of variation (the normalized second moment), of an appropriately defined inter-UE distance measure, and correlation coefficient (the normalized cross moment) between UE and BS locations, are adjusted to control the degree of heterogeneity and the bias towards the BS locations, respectively. This model is used in heterogeneous wireless cellular networks (HetNets) to demonstrate the impact of heterogeneous and BS-correlated traffic on the network performance. This network is called HetHetNet since it has two types of heterogeneity: heterogeneity in the infrastructure (supply), and heterogeneity in the spatial traffic distribution (demand).

Optimal Tradeoff Between Sum-Rate Efficiency and Jain's Fairness Index in Resource Allocation

The focus of this paper is on studying the tradeoff between the sum efficiency and Jains fairness index in general resource allocation problems. Such problems are frequently encountered in wireless communication systems with M users. Among the commonly-used methods to approach these problems is the one based on the α-fair policy. Analyzing this policy, it is shown that it does not necessarily achieve the optimal Efficiency-Jain tradeoff (EJT) except for the case of M=2 users. When the number of users M>2, it is shown that the gap between the efficiency achieved by the α-fair policy and that achieved by the optimal EJT policy for the same Jains index can be unbounded. Finding the optimal EJT corresponds to solving a family of potentially difficult non-convex optimization problems. To alleviate this difficulty, we derive sufficient conditions which are shown to be sharp and naturally satisfied in various radio resource allocation problems. These conditions provide us with a means for identifying cases in which finding the optimal EJT and the rate vectors that achieve it can be reformulated as convex optimization problems. The new formulations are used to devise computationally-efficient resource schedulers that enable the optimal EJT to be achieved for both quasi-static and ergodic time-varying communication scenarios. Analytical findings are confirmed by numerical examples.

MAC Performance of a 3GPP-LTE Multihop Cellular Network

Multihop cellular networks offer increased coverage and capacity compared to singlehop cells of the same size. This is not as huge as using more base stations (BS) instead of wireless relay nodes (RN), but by this way there is no need for a fixed network access to each node. Therefore a cost-efficient deployment is easily achieved (less CAPEX and OPEX). Even when the coverage of a BS is already quite good, relays help to increase the overall system capacity. This paper analyzes numerically with analytic background the multihop operation in the frequency division duplex mode and discusses the MAC-layer protocol performance for the 3GPP- LTE system. OFDMA with centrally controlled resource coordination is assumed here. By following the analytic model we show that for relaying, OFDMA resources are utilized effectively in time and frequency and provide good coverage and capacity results. Parameters like directional relay antennas, space or time division multiple access and relay antenna gain are studied.

Parallel operation of half- and full-duplex FDD in future multi-hop mobile radio networks

There are two basic duplexing schemes for present and future mobile radio networks, frequency-division duplex (FDD) and time-division duplex (TDD). In general each of these methods has its benefits and drawbacks. However, both schemes have their scenarios where they perform best. In future mobile radio systems typical wireless data communication will not only occur in metropolitan area scenarios like hotspots in airports, city centres, exhibition halls, etc., but also in wide area environments, e.g. a moving car in a rural environment. In general TDD is more appropriate for dense metropolitan area scenarios whereas FDD has benefits in wide area environments. If an FDD terminal which transmitted and received simultaneously, it would need an expensive duplex-filter, in order to separate UL and DL channels. Half-duplex terminals do not need such a filter. Therefore, half-duplex FDD appears to be attractive in terms of cost. A Relay is a promising concept for next generation systems. It allows enlarging the cell coverage range and is increasing the total cell capacity. A relay is not connected by wire, but works in a decode-and-forward principle and consequently is a cost-efficient alternative to base stations. This paper introduces a protocol to support parallel operation of half- and full-duplex FDD terminals in a relay capable system.

User-in-the-loop: spatial and temporal demand shaping for sustainable wireless networks

The demand for wireless access data rates is growing exponentially at a pace where supply cannot keep up with. Wireless resources (spectrum, time, space) are limited and shared, and transmission rates cannot be improved anymore solely with physical layer innovations. On the consumer side, flat rate type tariffs have established unnecessarily high expectations and often wasteful consumption. Dealing with congestion is unavoidable as a consequence of operating in a regime where demand is close to, equal to, or exceeding the supply. We can no longer assume that the current over-provisioning approach continues to be feasible. Complementary to the engineering for the growth of the supply side, this article focuses on the engineering for the control of the demand side. An approach referred to as the “user-in-the-loop” (UIL) is therefore motivated here. This article proposes spatial control, in which the user is encouraged to move to a less congested location, and temporal control, in which incentives (e.g., dynamic pricing) ensure that the user reduces (or postpones) his current data demand in case the network is congested. Results from a survey, which measures how willing a user is to respond to such control, are also presented. As users are modeled by a system-theoretic box in a closed-loop (control) system, they feature an input handle for incentives and an output handle for the reaction. Incentives can be progressive tariffs, reward programs, higher access rates, or even environmental (green) indicators. Incentives are tailored to the major Quality-of-Service (QoS) classes and help to shape the demand at the application layer-7 as well as at the user (“layer-8”). UIL can safely be applied in addition to other technologies, which are mainly for increasing the supplied capacity.

On retiming of multirate DSP algorithms

The retiming of DSP algorithms exhibiting multirate behavior is treated. Using the non-ordinary marked graph model and the reachability theory, we provide a new condition for valid retiming of multirate graphs. We show that for a graph with n nodes the reachability condition can be split into the reachability condition for the topologically-equivalent unit-rate graph (all rates set to one), and (n/sup 2/-n)/2 rate-dependent conditions. Using this property a class of equivalent graphs of reduced complexity is introduced which are equivalent in terms of retiming. Additionally, the circuit-based necessary condition for valid retiming of multirate graphs is extended for the sufficient part.

Analysis of 3GPP LTE-Advanced cell spectral efficiency

Multihop and multipoint transmissions are two of the main features towards an increased spectral efficiency for the LTE-Advanced mobile radio system. Fixed wireless relays with in-band backhauling are considered as a multihop technique in LTE-Advanced. Relays improve cell capacity and cell edge user performance depending on the deployment. In this paper, at first, results for the peak spectral efficiency of LTE-Advanced are presented and secondly, an analytical model to calculate the cell spectral efficiency of relay enhanced cell deployments in the context of the IMT-Advanced evaluation is presented. The developed model is applied to the LTE-Advanced system comparing different relay deployments with different frequency reuse schemes.

PCC: a modeling technique for mixed control/data flow systems

Many signal processing systems make use of event driven mechanisms-typically based on finite state machines (FSMs)-to control the operation of the computationally intensive (data flow) parts. The state machines in turn are often fueled by external inputs as well as by feedback from the signal processing portions of the system. Packet-based transmission systems are a good example for such a close interaction between data and control flow. For a smooth design flow with a maximum degree of modularity it is of crucial importance to be able to model the complete functionality of the system, containing both control and data flow, within one single design environment. While the degree of abstraction should be sufficiently high to model and simulate efficiently, the link to implementation has to be fully supported. For these reasons we developed a computational model that integrates the specification of control and data flow. It combines the notion of multirate dynamic data flow graphs with event driven process activation. Thus, it maintains the flexibility and expressive power of data flow representations while enabling designers to efficiently control these operations by incorporating control automata that may have been designed using protocol compilers or state machine tools.