Presented By Riaz (STD ID: 82081029) Proportional Fair Power Allocation with CDF-Based Scheduling for Fair and Efficient MU OFDM Systems System Group’s Seminar June, 2009 Presented before Professor Kyung Sup Kwak Presented By Riaz (STD ID: 82081029) Graduate School of Information Technology and Telecommunications Inha University, South Korea 19 April 2019

Telecom Engineering Lab, INHA University Reference Paper Title: Proportional Fair Power Allocation with CDF-Based Scheduling for Fair and Efficient Multiuser OFDM Systems Authors: Hanbyul Seo and Byeong Gi lee Journal: IEEE Transaction on Wireless Communications, Vol. 5, No. 5, May 2006 19 April 2019 Telecom Engineering Lab, INHA University

Telecom Engineering Lab, INHA University Contents Introduction System Model Opportunistic Subcarrier Allocation Proportional Fair Power Allocation Performance Comparison Conclusion 19 April 2019 Telecom Engineering Lab, INHA University

Telecom Engineering Lab, INHA University Introduction In Multiuser OFDM, it is important to allocate resources fairly among the users while maximizing the system efficiency. Shortcomings of recent works Improper to non-real time data services or Fairness aspect is not considered or Based on instant service rate In this paper, a new adaptive resource allocation scheme is proposed that can achieve fairness in terms of time-average throughput without zero-delay constraint, while maximizing the system efficiency For sabcarrier allocationCDF based scheduling. Tx power allocation proportional fair power allocation (PFPA): relative throughput-increment is identical in each subcarrier. 19 April 2019 Telecom Engineering Lab, INHA University

Telecom Engineering Lab, INHA University System Model (1) Consider, downlink transmission of a MU OFDM system BW=B, Number of orthogonal subcarrier=M Each MS measures the channel gain of each subcarrier and feeds back the CSI to BS Each subcarrier sees frequency flat fading and the channel gain remains constant during a slot but varies slot to slot SNR of the m-th sabcarrier signal of the k-th user at n-th slot can be expressed by allocated Tx power Channel gain PSD 19 April 2019 Telecom Engineering Lab, INHA University

Telecom Engineering Lab, INHA University System Model (2) In MU OFDM, resource allocation algorithm decides which user to serve with what power for each subcarrier. Here we assume the total Tx power constrained to S. Once the resources are allocated to users, the instant data rate of each user is determined and the BS serves each user at this rate. The instant service rate can be shown: Time-average throughput of each user: Indicator function 1 or 0 19 April 2019 Telecom Engineering Lab, INHA University

Telecom Engineering Lab, INHA University System Model (3) Throughput vector Achievable vector Is a throughput vector if it the algorithm can yield the throughput for user k Achievable Region Set of all achievable vectors Total Number of User 19 April 2019 Telecom Engineering Lab, INHA University

Opportunistic Subcarrier Allocation (1) For, MU diversity gain and increased overall system capacity We adopt CDF-based scheduling (CS) algorithm: possible to determine the performance of each user in an analytic manner CS selects a user as: Weighting factor CDF of channel gain Asymptotic behavior of channel gain of the user selected by CS: Sufficient to consider the case of MR algorithm with identical competing users. In this case, the channel gain of the selected user is given by Since gk’s are RV, selected channel gains are also random. If we assume Rayleigh fading channel, gk’s are i.i.d. exponential RV with mean g. So we can determine the distribution of selected channel gain which is a function of the number of competing users, K/, as well 19 April 2019 Telecom Engineering Lab, INHA University

Opportunistic Subcarrier Allocation (2) According to extreme value theorem, the asymptotic mean of selected channel gain: Gumbel RV distribution Effective Channel Gain Can be regarded as selected channel gain, since the normalized (by selected channel gain) error between it and the selected channel gain approaches zero 19 April 2019 Telecom Engineering Lab, INHA University

Opportunistic Subcarrier Allocation (3) Assume, M increases to infinity, for a given BW B. Selection probability, Pk= Number of selected subcarrier, nk The effective channel gain of kth user for the average channel gain Then by law of large of numbers, the relative number of allocated subcarrier nk/M approaches to the selection probability as M increases to infinity So asymptotic throughput of each user: Ratio of allocated power of kth user to total power S. 19 April 2019 Telecom Engineering Lab, INHA University

Proportional Fair Power Allocation (1) Conventional power allocation algorithms have some weakness that degrade the system performance when employed in heterogeneous user channel environment. EQ Algorithm: does not take the CSI of each subcarrier into consideration so it can not exploit the flexibility of Tx power which is inherent in MU OFDM sys. WF Algorithm: no fairness One may try to allocate many subcarriers to the users with low average channel gains, but it severely degrades the throughput of users in good channel condition In order to resolve the above problems Define a metric on the efficiency of using Tx power and then develop a new power allocation algorithm based on it. 19 April 2019 Telecom Engineering Lab, INHA University

Proportional Fair Power Allocation (2) The relative throughput increment of a subcarrier Or, the normalized increment of service rate contributed by the increment of power Then we consider a power allocation scheme such that the resulting is identical among all subcarriers. As this is a monotonically decreasing function of power, this scheme always allocates additional power to the subcarrier whose relative throughput-increment subject to power increment is the largest. Consequently this PFPA scheme maximizes the sum rate over all subcarriers and yields a proportional fair property. 19 April 2019 Telecom Engineering Lab, INHA University

Proportional Fair Power Allocation (3) In OFDM systems, the number of subcarrier is very large, so it may be too complex to calculate power allocation to each individual subcarrier based on PFPA. Two-tier approach: first allocate total power user-based (inter-user) and then distribute it subcarrier-based (intra-user). Inter-user: PFPA with effective channel gain Intra-user: EQ or WF Inter-user: if nk subcarriers are selected for user k, then the inter-user PA problem reduces to the problem of determining the amount of allocated power, , satisfying the condition: The amount of allocated power is determined by the avg channel gain and the number of assigned subcarrier, not by the instant channel gain of each subcarrier. 19 April 2019 Telecom Engineering Lab, INHA University

Proportional Fair Power Allocation (4) PFPA in the asymptotic case Asymptotic relative throughput-increment Asymptotically optimal resource allocation that exhibits the largest achievable region when the throughput of each user is given by (9). PA becomes equivalent to the PFPA also constant 19 April 2019 Telecom Engineering Lab, INHA University

Proportional Fair Power Allocation (5) Left hand side term indicates the amount of allocated power per allocated BW, which can be interpreted as Optimal PA is similar to the WF that regards as the channel gain. the difference is that the water level of PFPA is inversely proportional to , the throughput per allocated BW, while the water level of WF is constant for all users 19 April 2019 Telecom Engineering Lab, INHA University

Comparison: Achievable Region (case-1) Fig. 1 (a) 19 April 2019 Telecom Engineering Lab, INHA University

Comparison: Achievable Region (case-2) Fig. 1 (b) 19 April 2019 Telecom Engineering Lab, INHA University

Comparison: Amount of Allocated Resources Fig. 2 19 April 2019 Telecom Engineering Lab, INHA University

Comparison: Average Throughput Fig. 3 19 April 2019 Telecom Engineering Lab, INHA University

Comparison: Average Spectral Efficiency Fig. 4 19 April 2019 Telecom Engineering Lab, INHA University

Telecom Engineering Lab, INHA University Conclusion PFPA Algorithm is proposed. It allocates the additional power to the subcarrier whose relative through-put increment is the largest, which results in the proportional-fair allocation Proposed PFPA is equivalent to the asymptotically optimal PA algorithm. Results show PFPA algorithm outperforms conventional PA algorithms in terms of time-average throughput, in heterogeneous user channel environments Thanks for your cooperation Questions/Comments 19 April 2019 Telecom Engineering Lab, INHA University