Research On Cross-layer Design With Feedback Delay Information In Multiuser MIMO Systems

On the basis of multiple input multiple output (MIMO) technique, multiuser MIMO can makefull use of multi-antenna diversity and multiuser diversity to obtain superior performance. As a result,it provides better performance gain than single user MIMO system. Cross-layer design (CLD) canrealize optimal resources allocation and improve the overall performance of the system according tothe dynamic change in wireless network environment. In this thesis, by combining adaptivemodulation (AM) at physical layer and automatic repeat request (ARQ) as well as user scheduling atthe data link layer, the performance of CLD with feedback delay in multiuser MIMO system is wellinvestigated. Using the optimized CLD, the overall performance of system is enhanced greatly, whichwill have important theoretical significance and research value. The main contents in this thesis aresummarized as follows:1. The CLD based on multiple outdated estimates (MOE) in multiuser MIMO is studied. Bycombining AM, ARQ, antenna selection and user scheduling, the cross-layer design scheme withMOE and imperfect feedback is proposed. This scheme can avoid the performance loss of existingscheme with single outdated estimated method, and the resultant spectral efficiency (SE) and packeterror rate (PER) performance are effectively improved. Based on this, the closed-form expressions ofaverage SE and PER of the system are respectively derived, which will provide the effective methodfor the performance evaluation in theory.2. The CLD based on variable thresholds in multiuser MIMO system is investigated. To reducethe effect of delayed feedback, the variable thresholds (VTs) are derived by means of the maximum aposteriori method and the approximate PER expression. Based on this, the corresponding CLDscheme is presented. The proposed VTs can adapt to the change of delayed feedback information.Compared to the CLD with conventional fixed thresholds, the presented CLD with VTs has higherSE.3. The CLD and thresholds optimization in multiuser MIMO system subject to the average PERconstraint is studied. Conditioned on the given target PER, a CLD scheme based on the average PERconstraint is developed to maximize the SE of the system. The scheme can meet the requirement oftarget quality and improve the SE performance. By means of Karush-Kuhn-Tucker optimizationcondition, an effective iterative algorithm based on Newtown’s method is proposed to obtain theoptimal thresholds.