Jani Matti Johannes Moilanen

Comparison of Different Scheduling Algorithms for WiMAX Base Station: Deficit Round-Robin vs. Proportional Fair vs. Weighted Deficit Round-Robin

In this paper, we present a performance comparison of different WiMAX base station (BS) scheduling algorithms: deficit round-robin (DRR) vs. proportional fair (PF) vs. weighted deficit round-robin (WDRR). Our simulations show that when the radio channel conditions are taken into account (in PF and WDRR schedulers), the improvements in throughput can be considerable.

Active Queue Management for Reducing Downlink Delays in WiMAX

In WiMAX networks, the base station (BS) is a likely bottleneck for downlink (DL) TCP connections due to difference in available bandwidth between the fixed network and the wireless link. This may result in buffer overflows or excessive delays at the BS, as these buffers are connection-specific. In order to avoid buffer overflows, different active queue management (AQM) methods may be applied at the BS. This paper presents an analysis of several AQM mechanisms and proves that they are indeed very useful: AQM reduces considerably DL delays at the WiMAX BS without sacrificing TCP goodput.

Efficient Two-Dimensional Packing Algorithms for Mobile WiMAX

We present the result of research, developed within Nokia Siemens Networks, to solve the downlink sub-frame allocation problem in Mobile WiMAX (IEEE 802.16) technology in its full complexity, while simultaneously fulfilling real-life constraints on processing power and delay. We describe the IEEE 802.16 standard, and introduce two system models. A theoretical analysis of the two-dimensional packing problems originated by such models shows that they are both NP-hard in the strong sense. From a practical point of view, the processing budget for scheduling in the base station was estimated to be 1 ms on a state-of-the-art PC. Thus, we introduce two highly efficient heuristics that were developed to handle the system practically. A thorough computational analysis of their optimization characteristics and a system-level evaluation in realistic scenarios proved that the algorithms offer significant capacity gain in Mobile WiMAX systems that translate to increased operator revenues. This paper was accepted by Dimitris Bertsimas, optimization.

Flow Control for Multiflow in HSPA

Multiflow is a major enhancement envisioned as part of evolved HSPA. As 3GPP Release 11 is nearing its conclusion, Multiflow forms an integral element of the new set of standards. 3GPP compliant simulation studies from various stakeholders have shown a cell- edge throughput gain in the order of 40%. 3GPP simulation assumptions for Multiflow in release 11 however targeted an ideal scenario to quantify upper bound on achievable throughputs. Some of the key challenges related to Multiflow that have been identified as part of 3GPP work item include flow control between RNC and participating nodeBs, scheduling and distribution of data among the links, dynamic buffer management and the skew arising from an imperfect data split. Although, these issues have been widely discussed in the 3GPP context, there have been no extensive system level simulations so far to accurately study the constraints. This paper highlights such aspects by means of system level simulations. The paper also presents a framework for dynamic buffer management with flow control and the performance of different data split algorithms to combat skew. A comparison of the achievable throughput when an ideal data split is replaced with a realistic one is also investigated.

Load Balance for Multi-Layer Reuse Scenarios on Mobile WiMAX System

This paper intends to propose a novel handover algorithm to balance the load of the layers in a multi-reuse scenario. Each layer works independently from each other and it has its own scheduling process, coverage and mobile stations attached. The algorithm proposed balances the resources among layers by moving mobile stations from one to another layer according their QoS requirements and channel condition. Results show that it can increase the cell coverage and still keeping a satisfactory quality for the VoIP calls. Effective spectral efficiency also increased when comparing with single tri-sectorized reuse 1 scenario. The algorithm is also prepared to avoid ping-pong handovers and to work for any number of layers.

Alternative concepts of antenna deployment and cell layout in mobile communications

Cellular communication systems have traditionally been designed according to the paradigm that base stations serve independent sectors for which inter-sector interference should be minimized. Further, multiple base stations serving multiple sectors are traditionally grouped into a minimum number of sites, in order to reuse infrastructure for cooling, battery backup etc. and minimize site rental cost. Considering the current evolution of mobile communications, however, both the paradigm of avoiding interference and that of minimizing the number of sites may have to be revisited. For example, multi-cell transmission and reception schemes (i.e. such as Multiflow in HSPA or Coordinated Multi-Point (CoMP) in LTE-Advanced) provide the highest gains where cell overlap is maximized. Further, the development of active radio heads with significantly reduced cost, form factor, cooling requirements and simplified site acquisition may completely change the way in which cellular systems should be deployed. In this paper, we compare classical to alternative deployment concepts and evaluate these according to the achievable spectral efficiency per area, taking into consideration different assumptions regarding cost evolution. It is shown that especially rings of inward-pointing sectors can be an interesting alternative deployment strategy in the context of sector cooperation.

A Downlink MAC Frame Allocation Framework in IEEE 802.16e OFDMA: Design and Performance Evaluation

The IEEE 802.16e standard specifies a connection-oriented centralized Medium Access Control (MAC) protocol, based on Time Division Multiple Access (TDMA), which adds mobility support defined by the IEEE 802.16 standard for fixed broadband wireless access. To this end, Orthogonal Frequency Division Multiple Access (OFDMA) is specified as the air interface. In OFDMA, the MAC frame extends over two dimensions: time, in units of OFDMA symbols, and frequency, in units of logical sub-channels. The Base Station (BS) is responsible for allocating data into the frames so as to meet the Quality of Service (QoS) guarantees of the Mobile Stations’ (MSs) admitted connections. This is done on a frame-by-frame basis by defining the content of map messages, which advertise the position and shape of data regions reserved for transmission to/from MSs. We refer to the process of defining the content of map messages as frame allocation. Through a detailed analysis of the standard, we show that the latter is an overly complex task. We then propose a modular framework to solve the frame allocation problem, which decouples the constraints of data region allocation into the MAC frame, i.e. the definition of the position and shape of the data regions according to a set of scheduled grants, from the QoS requirements of connections. Allocation is carried out by means of the Sample Data Region Allocation algorithm (SDRA), which also supports Hybrid Automatic Repeat Request (H-ARQ), an optional feature of IEEE 802.16e. Finally, we evaluate the effectiveness of SDRA by means of Monte Carlo analysis in several scenarios, involving mixed Voice over IP (VoIP) and Best Effort (BE) MSs with varied modulations, with different sub-carrier permutations and frequency re-use plans.