Suwon Park

Orthogonal code hopping multiplexing

An orthogonal code hopping multiplexing scheme is proposed as a statistical multiplexing scheme for an orthogonal downlink in order to accommodate more orthogonal downlink channels than orthogonal codewords for mobile stations, and its performance is evaluated.

Log-likelihood ratio (LLR) conversion schemes in orthogonal code hopping multiplexing

Log-likelihood ratio (LLR) conversion schemes are proposed to reduce the effect of perforations that occur in orthogonal code hopping multiplexing (OCHM), which was previously proposed to accommodate more downlink channels than the number of orthogonal codewords. The proposed LLR conversion schemes greatly reduce the required signal-to-noise ratio (SNR) in channel decoding even when the perforation probability is high. The performance of the proposed schemes is evaluated by simulation in terms of the required E/sub b//N/sub 0/ for a 1% block error rate.

Capacity improvement in CDMA downlink with orthogonal code-hopping multiplexing

Orthogonal code-hopping multiplexing (OCHM) is a statistical multiplexing scheme designed to increase the number of allowable downlink channels in code division multiple access (CDMA) systems. OCHM is expected to compensate for a lack of codewords in future communication systems. In CDMA systems including OCHM, system capacity is limited by the number of codewords and power (or interference), and the maximum system capacity is determined by a stronger limitation between them. Call blockings due to power limitation may occur firstly if downlink channels demand large E/sub b//I/sub 0/ values and a high-channel activity. On the other hand, code limitation may occur prior to power limitation in CDMA. The maximum system capacities determined by both code and power limitations must be known, even in OCHM. However, previous studies on OCHM system capacity focused only on increasing the number of multiplexed users with no consideration of the power limitation. In this paper, the overall system capacity of OCHM considering both code and power limitations was evaluated. For this analysis, the transmission chip energy of base station (BS) and inner/outer-cell interference is mathematically derived in a multicell and multiuser environment. The downlink system capacity for OCHM is larger than for orthogonal code division multiplexing (OCDM) as other cell interference (OCI), mean channel activity, and the required E/sub b//I/sub 0/ value decrease.

Uplink transmit power control during soft handoff in DS/CDMA systems

In this paper we propose how to control the uplink transmit power of a mobile station (MS) during soft handoff in order to reduce the error probability of downlink transmit power control command bit without macro diversity gain at the base station controller (BSC). The uplink transmit power control is based on uplink transmit power control commands from all base stations (BS) belonging to the active set. The proposed scheme can be applied to third generation mobile communication systems since an MS receives uplink (UL) transmit power control bits (TPCB) from its base stations and sends a downlink (DL) transmit power control bit (TPCB) to them.

Collision mitigation by log-likelihood ratio (LLR) conversion in orthogonal code-hopping multiplexing

Log-likelihood ratio (LLR) conversion schemes are proposed to mitigate the effect of collisions (or perforations) that occur in orthogonal code-hopping multiplexing (OCHM), which was previously proposed to accommodate more downlink channels than the number of orthogonal codewords. The proposed LLR conversion schemes greatly reduce the required SNR in channel decoding even when the perforation probability is high. The perforation probability in some LLR conversion schemes is estimated and several estimation methods are proposed. An LLR conversion scheme without estimation of the perforation probability is also proposed to avoid accurate estimation. The performance of the proposed schemes is evaluated by simulation in terms of the required E/sub b//N/sub 0/ for a 1% block error rate (BLER).

Orthogonal code hopping multiplexing for downlink statistical multiplexing

For orthogonal downlink and statistical multiplexing, three modes of orthogonal code hopping multiplexing (OCHM) are proposed to accommodate more orthogonal downlink channels than orthogonal codewords for downlink channels, and they are compared. The performance comparison shows that the hybrid mode OCHM outperforms both the division mode and the hopping mode.

An energy efficient power control mechanism for base stations in mobile communication systems

The development of ICT (Information and Communication Technology) industry has emerged as one of the major sources of world energy consumption Especially, energy consumption on base station is a large portion of total energy consumption In this paper we study with energy efficient power control mechanism for base station in mobile communication systems. We proposed a efficient sector power control based on distance between base station and mobile node. Also we proposed a sleep mode energy control mechanism In sleep mode energy saving protocol, each sector monitors the number of user in sector cell. If number of mobile node falls down a given threshold in sector cell, base station shuts down power. Simulation demonstrate the Tx energy of proposed algorithms and the tradeoff between energy saving and cell coverage

Adaptive code rate for orthogonal code hopping multiplexing (OCHM) in synchronous downlink

We proposed an Orthogonal Code Hopping Multiplexing (OCHM) scheme as a new statistical multiplexing scheme in synchronous downlink. OCHM enables a large number of users to share a limited number of code channels through statistical multiplexing. In this paper, we obtain the optimal code rate in several traffic load environments by simulation and summarize the appropriate traffic load region for each code rate as the optimal code rate. An adaptive code rate control scheme is proposed and the base station adaptively changes the code rate according to traffic environments in order to save power.

Performance comparison of orthogonal code hopping multiplexing (OCHM) and HDR schemes in synchronous downlink

We previously proposed the orthogonal code hopping multiplexing (OCHM) scheme as a new statistical multiplexing scheme in synchronous downlink and applied the OCHM scheme to IS-95 and wideband CDMA. OCRM enables a large number of users to share the limited number of code channels through statistical multiplexing. In this paper, we compare OCHM with HDR through link-level simulation. OCHM outperforms HDR in medium and high mobility conditions, while HDR operates better in a low mobility condition.

LoRaCloud: LoRa platform on OpenStack

In this paper, we discuss the implementation of LoRa network server on OpenStack. LoRa is a type of low power wide area wireless network protocols for Internet of Thing applications. We restructured the operations of LoRa network server so it can be flexible and scalable by exploiting the system services provided by OpenStack. For validation, we have established an experimental system by using available open sources for LoRa terminal, LoRa gateway, and OpenStack.