User level performance evaluation of VoIP using ns-2

Voice over IP (VoIP) is gaining an ever increasing popularity. As such, it nowadays represents one of the most studied test applications in the performance evaluation of wireline and wireless networks. However, a sound performance analysis of VoIP communications should be carried out at the user level, by computing perceptive metrics like the Mean Opinion Score (MOS) or the EModel. In this paper, we present enhancements to the popular Network Simulator 2 (ns-2) that allow a reliable VoIP user-level performance analysis to be carried out through simulation. We show that computing performance measures at the IP level, which is usually done in ns-2, often leads to inaccurate results. Our code is publicly available at http://info.iet.unipi.it/~cng/ns2voip/

Bandwidth Allocation with Half-Duplex Stations in IEEE 802.16 Wireless Networks

IEEE 802.16 is a recent IEEE standard for broadband wireless access networks. In IEEE 802.16 networks, the Medium Access Control ( MAC) protocol is centralized and explicitly supports quality of service ( QoS). That is to say, access to the medium by a number of Subscriber Stations ( SSs) is centrally controlled by one Base Station ( BS), which is responsible for allocating bandwidth to several MAC connections in order to provide them with the negotiated QoS guarantees. However, although the network can be operated in Frequency Division Duplex ( FDD) mode ( that is, transmissions from the BS ( downlink) and SSs ( uplink) occur on separate frequency channels), the standard supports SSs with half- duplex capabilities. This means that they are equipped with a single radio transceiver which can be used either to transmit in the uplink direction or to receive in the downlink direction. This may severely hamper the capacity to support QoS. Therefore, in order to allocate bandwidth, an IEEE 802.16 BS has to solve two related issues: 1) how it can schedule bandwidth grants to SSs in order to meet the QoS requirements of their connections and 2) how it can coordinate the uplink and downlink scheduled grants so as to support half- duplex capabilities. In this paper, we derive sufficient conditions for a set of scheduled grants to be allocated so that the transmission of each half- duplex SS does not overlap with its reception. Based on this, we propose a grant allocation algorithm, namely, the Half- Duplex Allocation ( HDA) algorithm, which always produces a feasible grant allocation provided that the sufficient conditions are met. HDA has a computation complexity of O(n), where n is the number of grants to be allocated. Finally, we show that the definition of HDA allows us to address the two issues mentioned above by following a pipeline approach. This is when scheduling and allocation are implemented by separate and independently running algorithms, which are just loosely coupled with each other. We show via extensive simulations that the performance of SSs with half- duplex capabilities, in terms of the delay of real- time and non- real- time interactive traffic, using HDA almost perfectly matches that of full- duplex SSs, whereas an alternative approach, based on the static partitioning of half- duplex SSs into separate groups, which are allocated alternately, is shown to degrade the performance

System and method for providing a fast and optimized uplink and downlink scheduling algorithm for use in FDD communication systems with half-duplex stations

A system and method for scheduling uplink and downlink burst data transmissions for half-duplex terminals in a communication system. After the first half duplex terminal capacity allocation is scheduled for a plurality of half duplex terminals, all available second half duplex terminals are placed in the same relative order as that of the half duplex terminal first capacity allocation. An iterative process is used in order to determine a final second frame layout. Once a set of potential solutions are determined, one solution is selected, and a final second frame structure is determined

Flexible Scheduling for Real-Time Services in High-Speed Packet Access Cellular Networks

This paper presents the hybrid channel-aware and real-time scheduler (HY-CART) for UMTS high-speed packet access networks. The latter works for both downlink and uplink scheduling, with slightly different embodiments due to the different technology constraints. Its basic principle is to select users based on their channel conditions when the deadlines are far ahead: as the deadlines approach, they become progressively more important. Furthermore, resources for scheduled users are allocated sparingly, i.e. enough to serve packets whose deadline is actually near, so as to make room for a possibly larger number of simultaneous users, and keeping into account the user channel state. Simulative evaluation shows that HY-CART performs better than the previous work, allowing more users to be served with the same resources

Performance evaluation of power management for best effort applications

Abstract-Reduced energy consumption is a crucial aspect of mobile Broadband Wireless Access (BWA) networks, which are expected to be populated by battery-operated devices, like mobile phones and palmtops. For this reason the IEEE 802.16e specifies a set of power saving mechanisms to be employed by the Base Station (BS) and Mobile Stations (MSs) to concurrently reduce the amount of time the latter have the wireless interface on. The mechanisms are classified into three classes, which are designed for different types of applications. In this paper we focus on class I, which fits the typical requirements of best-effort traffic. With class I, an MS with power saving enabled alternates between sleep and listening periods. The duration of the sleep periods increases by a factor 2 each time a listening period ends, up to a maximum sleep window size. Since the standard does not provide guidelines for setting the above parameters, which are negotiated between the BS and MSs when setting up a power saving class, we evaluate via simulation their impact on the performance, in terms of both application-specific metric, i.e. delay or throughput depending on the type of traffic, and the amount of energy saved