LTE高密度小細胞網路使用多點協調傳輸技術之下行資源配置

Abstract

LTE為3GPP制訂的標準，是目前4G網路最具前景的科技之一，其目標為提供高速資料傳輸、彈性頻寬使用、減少傳輸延遲時間、以及支援高速移動傳輸等技術性服務。為了達成此目的，LTE在下行系統和上行系統分別使用OFDMA與SC-FDMA的編碼技術，使它能突破傳統無線網路技術上的限制，晉升為4G網路的一員。

多點協調是被3GPP視為ㄧ個很重要的技術，尤其是對於位在邊界的用戶，這項技術能夠有效的提升這些用戶的吞吐量以及可靠信，多點協調技術主要可以分為兩個項目，分別為Joint Transmission (JT)以及Coordinated Scheduling/Beamforming (CS/CB) ，在JT模式下合作的基地台可以同時服務一個相同的使用者，而在CS/CB模式中，每個基地台除了能服務原本自己下面的使用者外，還能服務合作群中的使用者。由於多點排程下的排程是相當的複雜，為了降低計算複雜度，我們進而提出啟發式的演算法，嘗試去逼近問題的最佳解。並且在模擬中也會根沒有使用多點協調技術來做比較，來看出使用這項技術的好處。

Long Term Evolution (LTE), one of most promising technology for 4G mobile networks, is the latest standard of 3rd Generation Partnership Project (3GPP). The goal of LTE is to provide high data rate transmission, flexible frequency usage, smaller latency, and supportable transmission in high mobility. To achieve this, LTE employs the modulation technique by OFDMA in downlink and SC-FDMA in uplink, breaking the technical limitations of traditional wireless, and makes itself be the one of members of 4G mobile networks.

Coordinated Multi-Point (CoMP) transmission and reception is one of the most promising technologies introduced in 3GPP standard. Expecially targeting the User Equipments (UEs) in the cell edge region, CoMP technology improves the edge throughput and reliabilityy in two ways: Joint Transmission (JT) and Coordinated Scheduling/Beamforming (CS/CB). With JT mode, the cooperating eNBs jointly serve a specific UE. With CS/CB mode, each eNB provides a service to the UE in the cooperating eNB group. Since the optimization problem of resource allocation in CoMP scheduling is NP-hard, we proposes an algorithm which allocates the frequency band to each UE and could operate in JT, CS/CB mode. We evaluate the proposed formulation and heuristic algorithms by conducting simulation. The performance of the proposed algorithm is comparatively evaluated along with that of other schemes such as non-coordination schemes.