Orlando Cabral

Spectrum Aggregation with Multi-band User Allocation over Two Frequency Bands

This paper seeks to explore the integration of spectrum and network resource management functionalities to the benefit of achieving higher performance and capacity gains in an IMT-A scenario. In particular, we investigate the allocation of users over two frequency bands (i.e., 2 GHz and 5 GHz ones) for a single operator scenario. The same type of RAT is considered for both frequency bands. It is assumed that the operator considered in this work has gained access to the frequency pool with a certain portion of the available spectrum. The operator has access to a non-shared 2 GHz band and to part (or all) of the frequency pool band at 5 GHz. The performance gain is analyzed in terms of higher data throughput, reduced delay and lower blocking probability. The performance is heavily dependent on the channel quality for each user in the considered bands which, in turn, is a function of the path loss and the distance from the base station (BS). The operator will have relevant improvements when user terminals are heterogeneously distributed on the cell, with variable distances from the BS. A gain up to 400 kbps (22%) was obtained with the proposed suboptimal solution.

QoS Metrics for Cross-Layer Design and Network Planning for B3G Systems

After 3G mobile and wireless systems take-up, the research community is now directing its interest towards unified ways of looking at system design, optimization, and quality of service (QoS) issues to satisfy the requirements of next generation multi-service mobile and wireless IP-based networks. Their implementation requires the development of IP QoS architecture and mechanisms encompassing the various layer of the OSI Model to cope with the new requirements. This work identifies the requirements on latency (link radio), latency (end-to-end), bit error rate, data rates, and traffic characterisation for mobile multimedia network beyond 3G. Characterisation parameters were identified and values were suggested for their range of variation, in the context of cross-layer design.

Multi-operator resource sharing scenario in the context of IMT-Advanced systems

This paper investigates and proposes a framework for the efficient integration of functionalities for dynamic spectrum use (e.g., spectrum aggregation) and cooperative radio resource management (RRM) in the scope of IMT-Advanced (IMT-A) candidate systems. The envisaged technical solution is based on a joint centralized and distributed approach for both intra-and inter-operator scenarios. Spectrum assignment decisions benefit from a distributed approach that can be realized by the pooling of resources at higher layers together. The paper investigates the possible interworking between the two techniques for the benefits of achieving higher performance and capacity gains. Based on the proposed framework, operators will be able to demand portions of the spectrum for a certain time period and coordinate this action with the actual network loads. The framework is described in terms of functionalities, physical entities, and mutual interactions. The proposed integrated framework can reduce the CAPEX and OPEX during the deployment of IMT-A systems.

Opportunistic load and spectrum management for mobile communications energy efficiency

Dynamic load and spectrum usage management techniques can significantly improve the energy efficiency of mobile communications systems. This paper considers: (i) the opportunistic reallocation of traffic loads between bands to allow radio network equipment in the bands that the traffic is originated from to be powered down, and (ii) the opportunistic selection of more appropriate spectrum based on propagation characteristics to minimize necessary transmission power through improving propagation and/or reducing power leaking into co-channel cells in frequency reuse cases. This paper addresses the simulation of video, FTP and HTTP (web browsing) traffic sources for configurations representing LTE and HSDPA telecommunications networks, and shows that the opportunistic reallocation of users between bands to power down radio equipment achieves a significant saving of 50% or more in from-the-socket power. Furthermore, it shows that the opportunistic reallocation of users/links to minimize transmission power through using more appropriate propagation spectrum leads to a further modest reduction in from-the-socket power consumption.

Optimization of multi-service IEEE802.11e block acknowledgement

Optimization of IEEE 802.11e MAC protocol performance is addressed by modifying several parameters left open in the standard, like block size and acknowledgement policies in order to improve the channel efficiency. The use of small block sizes leads to a high overhead caused by the negotiation on the other hand, the use of large block sizes causes long delays, which can affect negatively real-time applications (or delay sensitive applications). An event driven simulator was developed, and results with a single service and several services running simultaneously were extracted. By using the Block Acknowledgement (BA) procedure, for video and background traffics in a single service situation, the capacity was improved in the case when the number of stations is equal or higher than 16 and 12, respectively. However, for lower values of the number of stations, the use of BA leads to a slightly worst system performance. In a scenario with mixture of services the most advised block size is 12 (less delay in a highly loaded scenario). The number of supported user (total) increases from 30 to 35.

Optimal load suitability based RAT selection for HSDPA and IEEE 802.11e

Networks of the future envisage a network-of-wireless-networks that provide the end user the means to connect to the best available network at anytime and at any place. However, equally challenging for the operators is to provide these services at low cost in an era where spectral resources are a premium. This paper investigates cooperation between networks based Radio Access Technology (RAT) selection algorithm that uses suitability to optimize the choice between WiFi and High Speed Downlink Packet Access (HSDPA). It has been shown that this approach has the potential to provide gain by allocating a user terminal to the most preferred network based on traffic type and network load. Optimal load threshold values that maximise the total QoS throughput for the given interworking scenario are 0.6 and 0.53 for HSDPA and WiFi, respectively. This corresponds to a CRRM gain on throughput of 80% with 60 users.

Performance Evaluation and Traffic Modeling

Mobile and wireless communication systems are becoming more and more complex, making understanding the interaction of different technologies on different layers a very difficult task. The introduction of sophisticated techniques on the physical layer that react to changes of the wireless channel on small timescales requires new paradigms for modeling, simulating, and analyzing current and future wireless networks. Investigating the relationship of new physical layer techniques, application-specific requirements and performance measures will become a major research topic for future wireless networks. A continuous change in the methodology for evaluating the network performance takes place in the Internet. In the past, network performance was mainly evaluated using concretely measurable values like packet loss rate, delay, or jitter. The current trend in the Internet goes toward application-specific quality measures that judge more the subjective experience of the end user than they do network parameters. In the terminology, this is expressed as the change from quality of service (QoS-Quality of Service (QoS)) to quality of experience (QoE). For wireless networks this leads to interesting consequences, as currently the traffic requirements for MAC layer connections are mainly formulated in terms of QoS parameters. Accomplishing the change from QoS to QoE also in the definition of connection parameters is a future challenge for wireless networks, for which the first approaches are presented.

Service Suitability Based RAT Selection for Beyond 3G Systems

In beyond 3G systems, one of the important factors is to address radio access technology (RAT) selection and load balancing between heterogeneous networks to ensure high spectral efficiency in an era where spectral resources are at a premium. This work aims to address the feasibility of utilizing WiFi as complementary service for HSDPA, to prevent quality of service deterioration in the event of network overload in HSDPA during the busy period. The proposed RAT selection algorithm is based on the load of each system, and the results show that the outage probability can be improved by up to 45% relative to a stand-alone HSDPA system.

Implementation of IEEE 802.11e block acknowledgement policies based on the buffer size

Optimization of IEEE 802.11e MAC protocol performance is done by modifying several parameters left open in the standard, like buffer size and acknowledgement policies. By using the developed event-driven simulator, results were extracted with single and multi-service. With only a single service, higher values for the goodput are obtained for video and background (BK) traffics in comparison with the voice (VO) application. Besides, the number of supported user is higher for voice. With mixtures of traffic, when the number of station is small the goodput is lower for VO. However, for higher number of station, the lowest values for the goodput occur for background traffic. By using the Block Acknowledgement (ACK) procedure, for video and BK traffics, the capacity is improved when the number of station is equal or higher than 16 and 12, respectively. From a detailed analysis of the video application, a reduction of more than 40% was achieved in the delay. However, a clear trend is not identified for the optimum block size.

Urban cellular planning optimisation of multi-service enhanced UMTS based in economic issues

Results for Enhanced UMTS (E-UMTS) cost/revenue optimisation are obtained, as a function of the coverage distance, R. E-UMTS traffic generation and activity models are described and characterised in an urban scenario based on population and service penetration values. By using a System Level Simulator results were obtained for blocking and handover failure probabilities. Models for the supported fraction of active users and for the supported throughput, as a function of active users, were obtained. When one amplifier is used, the maximum throughput per BS is around 600kb/s. However, it achieves values up to 2000kb/s when three amplifiers per BS are considered. Generally, the profit in percentage is a decreasing function with R. The use of three amplifiers per BS is strongly advised in order to get cheaper communications, with prices that vary from 0.016 to 0.07 €/min, for R=250 and 1075m, respectively.