In cognitive radio networks, unlicensed users [secondary users (SU)] need to rendezvous on licensed channels before establishing communication links. Dedicated common control channel is the simplest way to achieve rendezvous. However, due to the absolute priority of licensed users [primary users (PU)] on accessing licensed channels, a dedicated common control channel may cause the PU long-time blocking problem, and the control channel saturation problem in a high SU density environment. Channel hopping schemes have been proposed to avoid the problems mentioned above. In this paper, we introduce two quorum-based channel hopping schemes. Our schemes outperform in terms of the four metrics: maximum time to rendezvous, channel loading, degree of rendezvous, and maximum conditional time to rendezvous.

Deploying femtocell networks embedded in the Macrocell coverage greatly benefits communication quality in variety manners. However, the lack of schemes to effectively mitigate detractive interference, fully utilize radio resources and provide quality-of-service (QoS) guarantee (in terms of delay) creates challenges to practically facilitate the concept of femtocell. To tackle these challenges to achieve a successful dense femtocell deployment, this paper proposes a cognitive radio resource management (CRRM) scheme which is inspired by the spirit of cognitive radio technology. Instead of the need of a centralized manner, the femtocell with the proposed CRRM can autonomously sense the radio resource usage of the Macrocell so as to mitigate interference. By analytical deriving the effective capacity of the CRRM that specifies the QoS guarantee capability of the system, the optimum sensing period and radio resource allocation are proposed for the CRRM to achieve a fully radio resource utilization while statistically guaranteeing the QoS of the femtocell. Numerical results demonstrate that the proposed CRRM outperforms the randomized scheme (without CRRM) in terms of the radio resource utilization efficiency. Simulation results also support the effectiveness on the delay guarantee performance.

It is not easy to achieve real-time video transmission testbed on WiMax, due to the lack availability of WiMax networks. This paper presents a ns-2 based emulator to evaluate the quality of multicast video services transmitted over an IEEE 802.16 wireless network. The impact of the modulation schemes and the cyclic prefix, on the throughput and video quality were discussed and the performance of the proposed emulator was evaluated. Specially, the results about the emulator's performance are relevant when real-time services are taken into account. The main contribution in this paper is the general guidelines provided to develop an efficient real-time multicast streaming video testbed on wireless networks, exploiting the potentialities of a tool as ns-2.

Based on IEEE 802.16 specifications, the convergence sublayer (CS) of 802.16-based networks provides the function for heterogeneous upper layer protocols. The CS can encapsulate such as IP packets with variable lengths or ATM cells with fixed length in its MAC PDU and usually adds a CRC-32 field to the rear of the MAC PDU. Based on the CRC-32, each 802.16 relay node or BS can detect error occurrence on a MAC PDU and use ARQ mechanism to retransmit the corrupt MAC PDU. However, for real-time streaming (e.g., UDP streaming), the ARQ mechanism is not required and the CRC-32 is also removed. Once CRC-32 is removed from the MAC PDUs, PDU error will not be detected by the intermediate nodes in time and these corrupt IP packets or ATM cells will be still forwarded in the networks to waste radio bandwidth. Hence, the error detection mechanism could be maintained, but the large overhead of CRC-32 should be reduced for real-time streaming. In this paper, we propose an efficient discrete-error-checking scheme (DECS) to reduce the overhead of error detection for real-time streaming. The proposed DECS only needs a few checking bits inserted in the MAC PDU, and it can efficiently provide the error detection function. Moreover, a chase mechanism concurrently works on each relay node and BS to early discard these corrupt and useless IP packets or ATM cells. The concept of the DECS including the chase mechanism can be extensively implemented in many wire and wireless multi-hop networks to further improve bandwidth utilization.

Cognitive radio (CR) technology is considered as an effective solution to enhance overall spectrum efficiency, especially primary radio network (PRN) typically having relatively low spectrum utilization. However, to realize CR concept, it is essential to provide enough incentives to PRN and extra profit to the service provider so that cognitive radio mobile stations (CR-MSs) may utilize PRN spectrum accordingly, which provides a new challenge for spectrum management. In this paper, we consider a PRN consisting of a primary system base station (PS-BS) and multiple primary system mobile stations (PS-MSs), and we therefore construct a cognitive radio network (CRN) consisting of a PRN with multiple CR-MSs. We propose a spectrum management policy framework such that CR-MSs can compete in utilization of the PRN spectrum bands available to opportunistic transmission of CR-MSs by Vickrey auction. PRN is granted incentives for being compensated for possible operating interference from CR-MSs in this scenario. Once CR-MSs are awarded the spectrum bands, they can be guaranteed a superframe time to utilize the spectrum band without any spectrum handoff. Consequently, in addition to incentives to the PRN, the overall spectrum utilization, the profit of the service provider, the spectrum access opportunity of the CR-MSs are increased to achieve co- win situation for every party in cognitive radio networks.