Árpád Drozdy

Resource management for QoS support in cognitive radio networks

Cognitive radio technology is a key enabler to reuse a finite, scarce, and expensive resource: the radio spectrum. Guaranteeing required levels of QoS to cognitive users and ensuring necessary protection to incumbent users are the two main challenges in opportunistic spectrum access. This article identifies the main requirements and challenges for QoS support in cognitive radio networks. A framework for a twofold cognitive manager is presented; one part managing spectrum availability on longer timescales and the other handling resource management on shorter timescales. This article gives particular focus to the functionalities of the latter cognitive manager related to resource management. Finally, we present a few key scenarios and describe how QoS can be managed with the proposed approach without disturbing the communications of incumbent users.

Bundling and multiplexing in packet based mobile backhaul

This paper investigates the bandwidth efficiency of packet based mobile backhaul in case of low rate, delay sensitive voice service. Evolved HSPA is a fully packet based mobile technology where the voice service is VoIP based. VoIP sources generate small packets periodically. The overhead on these packets is significant; it even exceeds the useful payload, causing efficiency problems on the mobile backhaul where bandwidth is still a scarce resource. A possible way to improve the efficiency of the voice service is to aggregate multiple voice packets into a single transport frame, a technique that reduces the relative overhead. This paper provides an overview of the available aggregation methods referred to as bundling and multiplexing. The performance of these solutions and their impact on the QoS of the voice service is investigated with simulations. Results show that if the backhaul is the bottleneck, the maximum number of VoIP connections that can be served jumps by up to 60%.

Adaptive VoIP Multiplexing in LTE Backhaul

LTE has a distributed system architecture optimized for IP connectivity. Circuit switched technology is not supported by LTE at all; therefore it provides VoIP based voice service only. In LTE, VoIP packets are carried with significant protocol overhead, thus transporting each voice packet separately is a waste of bandwidth. A possible way to improve the bandwidth efficiency of voice service over LTE is to multiplex the packets of parallel VoIP connections into a single transport frame. On the downside, multiplexing requires that some VoIP packets are retained which in turn will increase their end-to- end delay. This paper proposes a multiplexing method, which provides a good balance between bandwidth gain and quality of service by adapting its operation to the actual traffic mix. Three alternative solutions are proposed and investigated with simulations. The results show that VoIP multiplexing significantly improves the bandwidth efficiency of the voice service over LTE with only minor impact on the quality of service.

Diversity investigation of satellite backbone network for BFWA systems

The Broadband Fixed Wireless Access (BFWA) networks are terrestrial systems operating at high carrier frequencies (above 20 GHz), therefore one of the most harmful circumstantial factors in these systems is the attenuation caused by precipitation, especially by rain. Employing site diversity is a well-known method to improve the signal to interference plus noise ratio conditions within the BFWA network. The backbone of a BFWA can be wired or wireless terrestrial, however the connection between base stations and the operators core network can be also established by high frequency satellite links. Applying a satellite backbone system and route diversity between the Earth-space links can compensate precipitation attenuation. In this paper the efficiency of the diversity scheme in a satellite backbone network for BFWA system will be presented.

Adaptive QoS control in HSDPA systems

The high end-user data rates provided by HSDPA makes it a realistic alternative of wired Internet access. New 3GPP releases and the migration to packet based transport are further improving the capabilities of HSDPA. As a result, mobile data traffic is continuously increasing, various packet based services and applications with different QoS requirements are now accessible through HSDPA systems. This evolution requires efficient radio and transport QoS solutions and traffic differentiation methods. The HSDPA QoS framework specified by 3GPP and the air interface packet scheduling disciplines such as PF-RAD enforce the QoS and differentiation per connection level. In contrast, transport QoS architectures such as DiffServ are class based; differentiation is possible only per traffic aggregate level. The different approaches might result in inefficient system operation where the end-to-end QoS can be offered only by reducing the resource usage. This paper proposes a solution that aligns the operation of the transport and radio QoS mechanisms by continuously reconfiguring the transport schedulers. The performance of the proposed solution is investigated with simulations.