- Wednesday, 14 June, 11:00-12:30, Room Theatre Small Stage
- Session Chair: Hugo M Tullberg (Ericsson Research, Sweden)
Haris Celik and Ki Won Sung (KTH Royal Institute of Technology, Sweden)
Dynamic time-division duplexing (TDD) is considered a promising solution to deal with fast-varying traffic often found in ultra-densely deployed networks. At the same time, it generates more interference which may degrade the performance of some user equipment (UE). When base station (BS) utilization is low, some BSs may not have an UE to serve. Rather than going into sleep mode, the idle BSs can help nearby UEs using joint transmission. To deal with BS-to-BS interference, we introduce a new concept called joint transmission with dummy symbols where uplink BSs serving uplink UEs participate in the precoding. Since BSs are not aware of the uplink symbols beforehand, dummy symbols for nulling BS-to-BS interference are transmitted instead. Numerical results show significant performance gains for uplink and downlink at low and medium utilization. By varying the number of participating uplink BSs in the precoding, we also show that it is possible to successfully trade performance in the two directions.
Mary Adedoyin and Olabisi Emmanuel Falowo (University of Cape Town, South Africa)
In the fifth generation (5G) wireless networks, the heterogeneous deployment of ultra-dense small cells such as femtocells is seen as a major solution to cope with the exponential traffic growth and to improve coverage especially in indoor environments. However, the unplanned and ultra-dense deployment of femtocells in the coverage area of conventional macrocells introduces new challenges such as cross-tier interference (interference between macrocells and femtocells), co-tier interference (interference between neighbouring femtocells), and inadequate quality of service (QoS) provisioning, which can negatively affect the overall performance of the network. Hence, efficient radio resource management (RRM) algorithms are necessary to address these challenges. Therefore, in this paper, we propose a joint radio resource allocation with adaptive modulation and coding (AMC) scheme. The RRM problem is formulated as an optimization problem, which belongs to the class of mixed integer non-linear programming (MINLP). A reformation-linearization technique (RLT) is introduced to simplify the aforementioned MINLP. Finally, the performance of the proposed algorithm is evaluated and the simulation results show that the proposed algorithm reduces interference and enhances QoS in terms of the overall throughput and fairness when compared with other state-of-the-art algorithms.
Ikedieze Gabriel Anyim, John Chiverton, Misha Filip and Abdulkarim Tawfik (University of Portsmouth, United Kingdom (Great Britain))
Cognitive radio system is a context-aware technology in communications that offers Dynamic Spectrum Access. Spectrum sensing is an important function in the implementation of cognitive radio systems in detecting the presence or absence of primary users within the frequency spectrum and makes available free channels for secondary users. Cyclostationary Feature Detector is capable of detecting signals at low signal to noise ratios relying on the signal's features such as cyclic frequency, symbol rate, and carrier frequency and modulation type. Local oscillator frequency offsets, Doppler effects and jitter produce cyclic and sampling clock offsets at the receiver. We propose a multi-window cyclostationary feature detector that reduces these offsets by deriving the pair of window and fast Fourier transform sizes that can be used for implementation. Consequently, this pair was used to show that these offsets can be reduced and compared the detection performance with and without the offsets.
Sergio Lembo and Olav Tirkkonen (Aalto University, Finland); Mariana Goldhamer (Four G CelleX, Israel); Adrian Kliks (Poznan University of Technology, Poland)
We study the coexistence of FDD flexible duplexing systems, where a cellular network may use FDD uplink band for downlink transmission. As a result, adjacent channel emissions will change, with an effect to networks operating on adjacent channels. To stabilize the adjacent channel interference, equalizing downlink power control is considered, such that a flexible duplexing cell radiates in downlink a power density which is equivalent to the mean uplink transmit power of the cell. We derive a closed form equation for the transmit power, and evaluate coexistence performance in a heterogeneous network using the proposed power control.
Behnam Rouzbehani (Instituto Superior Técnico & GROW - Group for Research on Wireless, INOV - INESC Inovação, Portugal); Luis M. Correia (IST - University of Lisbon & INESC, Portugal); Luisa Caeiro (Escola Superior de Tecnologia de Setubal - Polytechnic Institute of Setubal, Portugal)
This paper proposes a model for radio resource management in virtualised radio access networks, based on the criterion of proportional fairness, which is also adapted to deal with the situations when there is not enough capacity to serve all subscribers with an acceptable level of service, the so-called the extreme case. A single virtual network operator providing four different classes of services negotiates the required capacity to serve its subscribers, from a centralised entity called Virtual Radio Resource Management (VRRM). The main goals of VRRM are to maximise the utilisation of resources, while maintaining a level of fairness in the allocation of data rate among different services. However, under extreme situations, the algorithm is modified to react differently, according to the offered traffic load. In general, it keeps serving a number of users having the stringiest Quality of Service (QoS), with the minimum guaranteed data rate, while the rest of users performing lowest QoS priority services are increasingly delayed. The performance of the proposed algorithm is evaluated through a practical heterogeneous network scenario and different evaluation metrics. Results show that when there is enough capacity, the algorithm is capable of satisfying the predefined service level agreements, while keeping fairness, whereas under extreme situations, it delays just enough number of users to free capacity for high priority services. In both cases, the algorithm is capable of maximising the utilisation of resources.