Research On Key Technologies Of Mobile Content Distribution

Voice was the major service of previous mobile networks.Mobile networks support E2E optimizations for voice on both architecture and protocols.Video centric content delivery is becoming the majority traffic of mobile network.The current network is not optimized for mobile content delivery.3GPP started CASD(Context Aware Service Delivery)study and standardization in 2016 for mobile context delivery optimization.The author participated into the work as one of the initiators.ETSI started MEC(Mobile Edge Computing)project for similar purpose a little earlier than 3GPP.The ongoing 5G design in 3GPP has accepted CASD and MEC as requirements.The big companies of internet industry e.g.Google,Akamai,China Cache,iQiyi started internet protocols(L4-L7)optimization for mobile content delivery as well.However,their optimized protocols are mutually incompatible and don't really resolve the issues in mobile content delivery.This these tries to improve mobile content delivery efficiency in a general applicable way by optimizing lower protocol layers(L1-L3)and mobile communication network architecture.The major problems of video centric mobile content delivery include:the current CDN cannot cache the content to the real edge node of mobile network,which leads to duplicated transmissions and long delay in backhaul;the current LTE broadcast mechanism is inefficient in small area broadcast due to inter-cell interference and lack of link adaption;ARQ/HARQ is proven to be very useful in unicast,however no cellular broadcast system found efficient way in supporting ARQ/HARQ for broadcast;the unicast retransmission mechanisms are partially duplicated with TCP,which lead to long latency and low efficiency;the TCP congestion control cannot adapt to fast radio channel variation,which leads to either low link utilization or long delay.With respect to these issues,this thesis designed optimizations on architecture and protocols for video delivery over mobile network,covering both unicast and broadcast delivery.The key contributions of this thesis are listed below,corresponding to chapter 2-5 respectively.1.Designed base station caching based mobile CDN architecture and mobile ICN(content centric network)architecture.The mobile CDN solution:UE assisted local caching,has been accepted by 3GPP as 4G standard in 2017.The gain of base station caching on user experience and cost saving are modelled and verified in this thesis.ICN is expected to be the technology of future internet.But,considering the scale of internet,fundamental protocol upgrade is super slow and difficult.The thesis designed HTTP over L2 to early introduce ICN concept into 5G mobile network.2.Based on the analysis on the limitations of existing LTE broadcast radio bearer types(MBSFN,SC-PTM),designed two new radio bearer types:SA-PTM(Small Area Point to Multi-point)and CoMP-PTM(Coordinated Multi-point PTM)for large number of receiving users and small number of receiving users respectively.The optimal bearer type selection is based on the counting for the number and distribution of receiving users.Existing cellular broadcast systems do not support efficient and accurate counting mechanisms due to concern in the cost of uplink feedback.This thesis proposes a novel power aggregared uplink sharing channel,like using MBSFN in UL.Based this channel,a physical layer counting mechanism and three detection algorithms are designed to accurately and efficiently count users,and then select optimal bearer type.3.Designed UL feedback channel sharing based broadcast HARQ,and RaptorQ based IR-ARQ(Incremental Redundancy ARQ)for efficient retransmission in broadcast.With respect to the duplicated and redundant retransmissions in different protocol layers of unicast content delivery,this thesis proposes cross-layer retransmission combining based on MAC reliability enhancement.4.Confirmed the congestion control issue of TCP over LTE unicast by simulation and designed two solutions:radio-aware TCP and HTTP over L2 for the issue.Based on the level of coupling between L2 and TCP,loose coupled solution and close coupled solution are proposed for radio-aware TCP.In loosed coupled solution,L2 information is provided to TCP for accurate congestion control.Close coupled solution replaces TCP congestion control with request-grant mechanism.Close coupled solution approaches to the theoretically performance limit of both link utilization and delay.As part of mobile ICN,HTTP over L2 removes TCP/IP from air interface,hence completely resolves the TCP issues.The value of the proposed solutions is confirmed by NS3 simulation.