IQ imbalance compensation for IFDMA systems

摘要

Interleaved frequency division multiple access (IFDMA) has drawn much attention and is standardized for uplink physical layer protocol in 3GPP LTE. IFDMA combines the advantages of single-carrier and multi-carrier solutions, i.e., it provides a low PAPR as well as low complexity for user separation. However, IFDMA is closely related to multi carrier transmission and hence, it is also expected to be sensitive to In-phase/Quadrature-phase (IQ) imbalance caused by the frequency conversion at the transceiver. In this report, first, we analyze the effect of transmitter (Tx) IQ imbalance at the received signal and show that the Tx IQ imbalance causes a serious interference at the received signal only between a certain pair of users. Making use of this fact, we propose a joint pairwise Tx IQ imbalance compensation and channel equalization scheme for IFDMA receivers. Linear receivers based on zero-forcing and minimum mean-square error criterion are proposed and both of them can be efficiently implemented in discrete frequency domain.%IFDMA（Interleaved frequency division multiple access）方式はシングルキャリアとマルチキャリアの特長を併せ持つ多元接続方式で，その低いピーク対平均電力比から，3GPP LTEの上り回線の通信方式の一つとして標準化されるなど近年高い注目を集めている．一方，周波数アップ/ダウンコンバージョンで発生するIQ不均衡は直交周波数分割多元接続（OFDMA）方式などで大きな特性劣化の要因となることが知られているが，マルチキャリアとしての側面も持つIFDMAに串いても同様の劣化を引き起こすと考えられる．本報告では，IFDMAにおける送信IQ不均衡の影響を考察し，IQ不均衡が特定のユーザー間にのみ深刻なユーザー間干渉を引き起こすことを明らかにする．また，その関係性を利用し，IFDMAのためのゼロフォーシング及び最小二乗誤差基準に基づく簡易な周波数領域等化及びIQ不均衡補償法を提案する.