Jong-Hyung Kwun

Non-orthogonal Multiple Access in a Downlink Multiuser Beamforming System

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 users 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.

Hard Handoff Scheme Exploiting Uplink and Downlink Signals in IEEE 802.16e Systems

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

Uplink NOMA with Multi-Antenna

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.

VoIP Scheduling Algorithm for AMR Speech Codec in IEEE 802.16e/m 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).

Noncoherent adaptive code synchronization for DS/CDMA systems

In this paper, a noncoherent adaptive code acquisition scheme is proposed by combining an adaptive filter with a differential detector. The carrier phase offset in the PN signal component of the filter input is removed by a differential detector. The probabilities for detection and false alarm are derived, and the mean acquisition time is evaluated under AWGN channel. The performance of the proposed system is compared with the conventional system using a matched filter. Simulation results show that the proposed system has a good performance under overall channel conditions, especially at low SNR. And the proposed system outperforms the matched filter by 4-6 dB under AWGN channel for 16 taps, as measured by the mean acquisition time.

End-to-End QoS Model for Mobile WiMAX Systems

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.

A handover time negotiation mechanism for seamless service in IEEE 802.16E

IEEE 802.16e specification adopted that a target base station (BS) transmits Fast_Ranging_IE() to the upcoming handover MS to reduce the handover interruption time. However, the handover interruption time can be increased if the MS fails to receive Fast_Ranging_IE() because the channel release time between the MS and the serving BS is increased more than the estimated handover time due to the queuing delay and the handover message loss. In this paper, we propose the handover time negotiation mechanism to receive Fast_Ranging_IE() exactly. The proposed mechanism helps the serving BS and neighbor BSs to negotiate and share the estimated handover time information each other. To determine the estimated handover time, we considers the queuing delay in wireless and wired network, and the delay due to the handover message loss. The simulation results show that the receiving failure ratio of Fast_Ranging_IE() is reduced about 94% and handover interruption time of 95% users is less than 150 m sec when the proposed mechanism is applied to IEEE 802.16e system. Therefore, the proposed mechanism helps the IEEE 802.16e system to support the seamless service for the real-time applications.

An MPI mitigation technique for high order data modulations in the presence of intracell interference

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.

An Efficient Uplink Scheduling Algorithm with Variable Grant-Interval for VoIP Service in BWA Systems

This letter proposes an efficient uplink scheduling algorithm for the voice over Internet protocol (VoIP) service with variable frame-duration according to the voice activity in IEEE 802.16e/m systems. The proposed algorithm dynamically changes the grant-interval to save the uplink bandwidth, and it uses the random access scheme when the voice activity changes from silent-period to talk-spurt. Numerical results show that the proposed algorithm can increase the VoIP capacity by 26 percent compared to the conventional extended real-time polling service (ertPS).

WLC32-6: A Cell Search Technique based on Known Postfix for OFDM Cellular Systems

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.