In this paper, we propose a non-orthogonal multiple access-based multiuser beamforming (NOMA-BF) system designed to enhance the sum capacity. In the proposed NOMA-BF system, a single BF vector is ...shared by two users, so that the number of supportable users can be increased. However, sharing a BF vector leads to interference from other beams as well as from the other user sharing the BF vector. Therefore, to reduce interference and improve the sum capacity, we additionally propose a clustering and power allocation algorithm. This clustering algorithm, which selects two users with high correlation and a large gain-difference between their channels, can reduce the interference from other beams and from the other user as well. Furthermore, power allocation ensures that each user's transmit power is allocated so as to maximize the sum capacity. Numerical results verify that the proposed NOMA-BF system improves the sum capacity, compared to the conventional multiuser BF system.
In this paper, we propose a uplink (UL) non-orthogonal multiple access (NOMA) systems equipped with multiple antennas to enhance the sum capacity of UL. In the proposed UL NOMA system, a base station ...(BS) with N antennas can support 2N users by sharing the space resource. However, sharing the space resource leads to interference between users. Therefore, to mitigate the interference and improve the sum capacity, we additionally propose a set selection algorithm and power control scheme. The set selection algorithm, which selects 2N users based on orthogonality and gain-difference between their channels, reduces the interference between users. Furthermore, the power control scheme can maximize the sum capacity with ensuring minimum target rate. Numerical results show that the proposed system improves the sum capacity over that of the conventional orthogonal multiple access (OMA) system.
This letter proposes an efficient uplink scheduling algorithm for voice over Internet protocol (VoIP) services with adaptive multi-rate (AMR) speech codec in IEEE 802.16e/m systems. The proposed ...scheduling algorithm adopts the random access scheme during silent-period to reduce the waste of uplink bandwidth considering the characteristics of AMR speech codec. The numerical results show that the proposed algorithm can increase the maximum supportable number of voice users by 26% compared to the conventional extended real-time polling service (ertPS).
In this paper, we propose a load balancing and a dynamic overlay clustering procedures including the fusion procedure. The proposed load balancing gets some loss for the throughput of the overall ...system but it improves the throughput of the cell-edge users. Through the simulations, we verify that the load and the number of users of the proposed system are changed uniformly. In addition, we demonstrate that the proposed system can improve the quality of service for cell-edge users while guaranteeing user fairness.
We consider hard handoff scheme based on uplink and downlink signals in IEEE 802.16e systems. To exploit the channel reciprocity in TDD systems, the proposed scheme triggers handoff initiation ...process using uplink signal. A serving base station monitors uplink traffic signal and triggers handoff process when the uplink signal strength or SINR becomes less than the predetermined level. This process can prevent mobile stations from periodically monitoring and reporting downlink signals of neighbor base stations at the non-handoff region. In the handoff decision process, the proposed scheme exploits not only uplink signal but also downlink signal as the handoff criteria to reduce ping-pong and outage probability. To efficiently combine uplink and downlink signal levels, the proposed scheme adopt an uplink and downlink joint hysteresis to determine a handoff direction. Using the joint hysteresis can reduce the outage probability compared with using uplink and downlink hysteresis independently. We evaluate the performance of the proposed scheme using computer simulation. The simulation results show that the proposed algorithm has better performance than the conventional mobile assisted handoff scheme of IEEE 802.16e in terms of the average number of handoff and the outage probability during handoff
End-to-End QoS Model for Mobile WiMAX Systems Sunghyun Cho; Jae-Hyun Kim; Jonghyung Kwun
2011 IEEE 35th Annual Computer Software and Applications Conference Workshops,
2011-July
Conference Proceeding
This paper defines an end-to-end QoS functional model for mobile WiMAX systems and investigate several technical issues. Our main contribution is to analyze the end-to-end QoS variations in mobile ...WiMAX systems according to the QoS functions. We discuss the strong and weak points of QoS related functions, which can be affected by the network architecture, and propose the design examples of a service class mapping function. To evaluate the end-to-end QoS, we implemented an end-to-end performance analysis simulator of mobile WiMAX using OPNET. Simulation results show that the uplink application layer throughput is about 70 percent of the uplink physical layer throughput.
Conventional frequency offset estimation algorithms require high computational complexity and redundant memory. We propose a simple carrier synchronization algorithm which can jointly estimate the ...frequency and phase offset, and compare the performance of the proposed algorithm with that of other algorithms. The proposed algorithm requires no hardware memory. The computational complexity of the proposed algorithm is low. The principle of the proposed algorithm is based on frequency domain analysis and an interpolation technique. The proposed algorithm is asymptotically unbiased, according to the numerical derivation. Simulation results show that the estimation accuracy of the proposed algorithm is close to the CRB even when E/sub b//N/sub o/ is as low as 0 dB.
Increasing throughput using high order data modulations in downlink WCDMA systems requires the elimination of the multipath interference (MPI). Linear chip equalizers using zero forcing (ZF) and ...minimum mean square error (MMSE) were proposed in downlink. A multipath interference canceller (MPIC) using weighted multi-stage parallel interference cancellation (PIC) was introduced in high speed downlink packet access (HSDPA) systems. We propose a multipath interference mitigation algorithm which removes the MPI in the presence of intracell interference. The proposed algorithm employs a linear tentative decision device with null zone in order to eliminate the MPI for intracell interference. As the intracell interference power increases, the proposed algorithm exhibits better performance compared with the RAKE and the MPIC.
A noncoherent adaptive code acquisition scheme is proposed by employing a differential detection technique. The carrier phase offset in the PN signal component of the filter input is removed by a ...differential detector. The numerical results for the detection and false alarm probabilities, and the mean acquisition time are derived. The performance of the proposed system is verified by simulations. The proposed system is compared with the conventional system using a matched filter by considering the mean acquisition time and the false alarm probability simultaneously. Simulation results show that the proposed system has a good performance under overall channel conditions, especially at low SNR, and outperforms the matched filter by 4-6 dB under an AWGN channel for 16 taps.
A cell search technique utilizing a known postfix for OFDM (orthogonal frequency division multiplexing) cellular systems is described. The known postfix is generated in the time domain by inserting ...pilots in the frequency domain and plays the role of the cyclic prefix in general OFDM systems. Since it demonstrates good correlation properties, it can be facilitated to synchronize each symbol with an identified postfix. In this paper, two different known postfixes are allocated to each cell. One is used for cell identification and symbol synchronization, which is designed to be different among neighboring cells. The other is used for frame synchronization and is the same for all cells. In the simulation, the cell search is accomplished with a probability greater than 10 -3 at -27 dB in a vehicular channel. Even at -30 dB, the cell search probability is greater than 10 -2 in a pedestrian channel as well as 10 -3 in the AWGN (additive white Gaussian noise) channel.
