• 한국통신학회논문지
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• 제36권6A호
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• pp.601-608
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• 2011

기존에 연구된 OFDMA(Orthogonal Frequency Division Multiple Access) 기반 다중 홉 전송망의 부반송파 페어링 방법들은 단순히 채널의 신호대잡음비(SNR)만을 고려한 것이므로, 2차 시스템의 사용으로 인해 1차 사용자에게 미치는 간섭량을 고려해야 하는 무선 인지 환경에는 적합하지 않다. 따라서, 본 논문은 OFDMA 기반의 다중 홉 무선 인지 시스템에서 1차 사용자에게 미치는 간섭을 제거하기 위해 전력제어를 수행할 경우, 감소된 수율을 향상시키기 위한 효과적인 부반송파 할당 방법에 관해 연구를 수행하였다. 간섭 채널 이득만을 고려한 IT(Interference channel gain) 방법과 채널 이득과 간섭 채널 이득의 비를 고려한 CI(Channel SNR over interference channel gain) 방법, 2가지의 부반송파 페어링 방법을 제안했으며, 모의실험을 통해 기존 방법과 성능비교를 수행하였다. 무선 인지 시스템에서 간섭 임계치를 만족시키기 위해 전력 제어가 필요한 경우에는 제안한 CI 방법이 성능이 가장 우수했으며, 기존 방법보다 최대 약 10% 이상의 수율 향상을 거두는 것을 확인하였다.

• 전기전자학회논문지
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• 제24권1호
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• pp.360-363
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• 2020

We present the power of the correlated superposition coding (SC) in non-orthogonal multiple access (NOMA). This paper derives closed-form expressions for the total allocated power with the constant total transmitted power. It is shown that the total allocated power is the function of a correlation coefficient. In result, the correlated SC NOMA should be designed with consideration of the correlation coefficient.

• 한국통신학회논문지
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• 제35권7A호
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• pp.682-687
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• 2010

The IEEE 802.15.4a specification targets the low-rate (LR) Impulse-radio (IR) ultra-wideband (UWB) system which is now widely applied in the WPANs considering rather short distance communications with low complexity and power consumption. The physical (PHY) layer uses concatenated coding with mixed binary phase-shift keying and binary pulse-position modulation (BPSK-BPPM), and direct sequence spreading with time hopping in order that both coherent and non-coherent receiver architectures are supported. In this paper, the performances of multiple access schemes compliant with IEEE 802.15.4a specification are investigated with energy detection receiver, which allow avoiding the complex channel estimation needed by a coherent receiver. However, the performance of energy detection receiver is severely degraded by multi-user interference (MUI), which largely diminishes one of the most fascinating advantages of UWB, namely robustness to MUI as well as the possibility to allow parallel transmissions. So as to improve the performance of multiple access schemes, we propose to apply the novel TH sequences as well as to increase the number of TH positions. The simulation results show that our novel multiple access schemes significantly improve the performance against MUI.

• 대한전기학회논문지:시스템및제어부문D
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• 제54권8호
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• pp.498-500
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• 2005

In a CDMA system, the capacity is variable and mainly depends on multiple access interference. The multiple access interference has a deep relationship with transmitted or received power The capacity of CDMA2000 1x system is considered to be limited by the forward link capacity Different rate data traffic requires different transmitted power and rate controlling enables the system utilize radio resource more efficiently. A very simple rate control algorithm for data calls in CDMA2000 1x system is proposed. In the proposed algorithm, by monitoring the total transmit power, we can simply adjust data rate to channel conditions and efficiently use radio resources. The proposed algorithm is easy to implement in power controlled CDMA systems.

• Journal of Communications and Networks
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• 제8권2호
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• pp.220-227
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• 2006

In this paper, we present a novel approach to analyze the throughput of direct-sequence spread spectrum multiple access (DS/SSMA) unslotted ALOHA system. In the unslotted system, the departure rate of interfering transmissions is proportional to the number of current interferers that can be regarded as the system state. In order to model this state-dependency, we introduce a two-dimensional state transition model that describes the state transition of the system. This model provides a more rigorous analysis tool for the DS/SSMA unslotted ALOHA systems with both fixed and variable packet lengths. Numerical results reveal that this analysis yields an accurate system performance that coincides with the simulation results. Throughout the analysis we have discovered that the state-dependency of the departure rate causes interference averaging effect in the unslotted system and that this effect yields a higher throughput for the unslotted system than for the slotted system when supported by a strong channel coding.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 심포지엄 논문집 정보 및 제어부문
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• pp.221-223
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• 2005

In a CDMA system, the capacity is variable and mainly depends on multiple access interference. The multiple access interference has a deep relationship with transmitted or received power. The capacity of CDMA2000 1x system is considered to be limited by the forward link capacity. Different rate data traffic requires different transmitted power and rate controlling enables the system utilize radio resource more efficiently. A very simple rate control algorithm fer data calls in CDMA2000 1x system is proposed. In the proposed algorithm, by monitoring the total transmit power, we can simply adjust data rate to channel conditions and efficiently use radio resources. The proposed algorithm is easy to implement in power controlled CDMA systems.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -3
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• pp.1952-1955
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• 2002

Multiple access interference (MAI) and multi path interference(MPI) degrades the system performance in the DS-CDMA(direct-sequence code-division multiple- access)systems .0 this paper, a generalized construction method fer 2$\^$n/(n=1,2,3) phase preferred pairs(PP) with zero-correlation duration (ZCD) of (0.5N+1) chips is proposed. 2$\^$n/(n=1,2,3) phase ZCD code sets with ZCD and enlarged family sizes are generated by carrying out a chip-shift operation of the preferred pairs . The properties of the proposed codes are effective for the cancellation of MAI and MPI in DS-CDMA Systems.

• 한국전자파학회논문지
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• 제13권7호
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• pp.641-648
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• 2002

The study on the chip waveform design to minimize multiple-access interference (MAI) and its performance evaluation are very important since chip waveform decides the signal quality and system capacity of the direct-sequence CDMA wireless communication system. This paper suggests the analytical chip waveform to minimize the MAI. The BER and throughput performances achieved by the proposed analytical optimum chip waveform are compared with those of the conventional chip waveforms in the Nakagami-m distribution frequency selective channel when the differential phase shift keying (DPSK) is employed in DS-CDMA system. From the numerical results, capacity and throughput are improved about 2 times and 1.4 times respectively when it is compared with the Kaiser chip waveform that is considered as one of the best in the conventional ones.

• 한국통신학회논문지
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• 제29권9B호
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• pp.771-777
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• 2004

In a COMA system, the capacity is variable and mainly depends on multiple access interference. The multiple access interference has a deep relationship with transmitted or received power. The capacity of COMA2000 system is considered to be limited by the forward link capacity. In this paper, we show that the forward link cell load can be represented by the total transmitted power of base station and we propose a forward link call admission control (CAC) strategy for COMA2000 system. The proposed call admission scheme adopts the rate control algorithm for data call. This call admission scheme enables the system to utilize radio resource dynamically by controlling data rate according to the cell load status, and enhance the system throughput and grade of service (GoS). quality of service(QoS) such as blocking and outage probability.

• 전기전자학회논문지
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• 제23권1호
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• pp.314-317
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• 2019

Recently, the symmetric superposition coding (SSC) [3] is proposed for a solution for the error propagation (EP) due to the non-perfect successive interference cancelation (SIC) in non-orthogonal multiple access (NOMA). We analyze the performance of NOMA with the SSC. It is shown that the performance of the SSC NOMA is the same as that of NOMA with the normal superposition coding (NSC) for the power allocation factor less than 20%, the SSC NOMA performance is better than the NSC NOMA performance up to the power allocation factor 80%, and the SSC NOMA performs worse than the NSC NOMA for the power allocation factor greater than 80%. As a result, the SSC should be used with consideration of the power allocation.