Relays in Heterogeneous Networks Submitted by: Arjun Bhatia Girish Anand Rajesh Gupta Shivani Bhatia Sunanda Mukundan University of Maryland, ENTS, Adv. Wireless Networks

Table of Contents Introduction Heterogeneous Networks Relays Implementation of Relays Types of Relays Implementation Strategies Handover Deployment Challenges Interference Management Economic Benefits References University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Path towards LTE Advanced The very high data rates and large coverage area envisioned for 4G wireless systems in reasonably large areas do not appear to be feasible with the conventional cellular architecture as : They do not achieve the expected throughput to ensure seamless mobile broadband in the uplink as users move far from the base station Increase in the inter-cell interference, as well as constraints on the transmit power of the mobile devices Poor indoor penetration and the presence of dead-spots, which results in drastically reduced indoor coverage Solution : To address these issues, there has been an increasing interest to deploy relays, distributed antennas and small cellular access points in residential homes, subways and offices. PS: Deployment of more number of BTS requires cost and planning Fall 2011 University of Maryland, ENTS, Adv. Wireless Networks

Heterogeneous Networks Network architectures with relays, picocells and femtocells overlaying the macrocell network are commonly referred as heterogeneous networks All these nodes have different characteristics of RF power and coverage area Nodes with large RF coverage area are deployed in a planned way to provide coverage in urban, suburban and rural areas For small coverage area, nodes provide coverage extension or throughput enhancement. By shrinking coverage to smaller blocks, the capacity can be shared with a fewer number of people, resulting in higher capacity and faster data speeds Fall 2011 University of Maryland, ENTS, Adv. Wireless Networks

Relay : Background A solution for radio range extension in mobile and wireless broadband cellular networks Time-division multiple access (TDMA)-based systems This scheme of relaying, allows for easy allocation of resources to the mobile-to-relay and relay-to-mobile links. The first system based on time-division multiplex (TDM) and relays connecting mobiles to the fixed network was proposed in 1985 Code-division multiple access (CDMA)-based systems Relaying in cellular CDMA systems has also been investigated by companies FDD based relay systems Uplink and Downlink are separated using frequency division duplex (FDD), as is done in IS-95 and Universal Mobile Telecommunications System (UMTS) terrestrial radio access (UTRA) FDD Fixed relays (called wireless BSs) for cordless systems The European Telecommunications Standards Institute/Digital Enhanced Cordless Telephony ( E T S I /DECT ) standard in 1998 was the first specifying fixed relays (called wireless BSs) for cordless systems using TDM channels for voice and data communications University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

RELAY NODES Relays are expected to be a cost efficient way to fulfill requirements on high data rate coverage in next generation cellular networks, like LTE-Advanced. Low-cost low transmit power base stations using the same spectrum as backhaul and access. And have similar power as Picos. Enhance performance at the cell edge for a comparatively low cost. Include peak data rates of 1 Gbps in downlink (DL) and 500 Mbps in uplink (UL), bandwidth scalability up to 100 MHz Fall 2011 University of Maryland, ENTS, Adv. Wireless Networks

Why Relays are Required Increased broadband Traffic : Increased traffic due to new applications Increased capacity : Number of mobile users with high-end smart phones accessing social networking, video and VoIP are increasing Provide High data rate : Path towards LTE- advanced, common convergence network Easy Installation : Het-Nets are being deployed initially in high data traffic areas using street-level plug-and-play nodes Low Cost : Relays can be even more cost-effective than a WLAN access point, as the former does not require a wired backhaul connection Low Opex cost : Reducing operating expenses such as tower leasing and maintenance costs for the service provider Work well in Non Line-of-sight operation : The spectrum that will be released for 4G systems will almost certainly be located well above the 2 GHz band. Therefore the radio propogation in these bands is significantly more vulnerable to non LOS conditions. Fall 2011 University of Maryland, ENTS, Adv. Wireless Networks

Advantages of Relays Transmission power of user equipment and base stations can be reduced More radio resources can be allocated to a single user – Hence improved capacity Spectrum efficiency per meter square would be improved Higher mobility and Quality of Service to the end users Relaying is presented as a means to reduce infrastructure deployment costs Exploitation of spatial diversity, multihop relaying can enhance cellular capacity – possible to connect BTS and relay at the same time Networks applying relaying via fixed infrastructure do not need complicated distributed routing algorithms, while retaining the flexibility of being able to move the relays as the traffic patterns change over time Solutions to combat shadowing at high radio frequencies University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Relays: Network Improvement Increase network density : LTE relay nodes can be deployed very easily in situations where the aim is to increase network capacity by increasing the number of eNBs to ensure good signal levels are received by all users. LTE relays are easy to install as they require no separate backhaul and they are small enabling them to be installed in many convenient areas, e.g. on street lamps, on walls, etc. University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Relays: Network Improvement Network coverage extension :   LTE relays can be used as a convenient method of filling small holes in coverage. With no need to install a complete base station, the relay can be quickly installed so that it fills in the coverage blackspot. University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Relays: Network Improvement LTE relay nodes may be used to increase the coverage outside main area. With suitable high gain antennas and also if antenna for the link to the donor eNB is placed in a suitable location it will be able to maintain good communications and provide the required coverage extension. University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Relays: Network Improvement Rapid network roll-out: Without the need to install backhaul, or possibly install large masts, LTE relays can provide a very easy method of extending coverage during the early roll-out of a network. More traditional eNBs may be installed later as the traffic volumes increase. University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Relay : Improve shadowing effect University of Maryland, ENTs, Adv. Wireless Networks

Relay Types Conventional Amplifiers : Relays are of two types : Decode and Forward Conventional Amplifiers :   Used as gap fillers. Also known as repeaters Fall 2011 University of Maryland, ENTS, Adv. Wireless Networks

Benefits: Limitations: Amplify the desired signals, like repeaters Perform better than Decode and Forward relays near the receiver Limitations: Analog repeaters increase the noise level and suffer from the danger of instability due to their fixed gain. Also amplify both the noise and interference Suffer from Loop Interference, i.e. leakage of transmit signals to receive antenna Concurrent transmission and reception at the same frequency band requires two separated antennas in the relay University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Decode and forward Remove the noise by decoding the received signals and then regenerating and re-encoding the signal to be forwarded to the destination Adaptive Decode and Forward Relay: The relay forwards the signal to the destination only if it is able to decode the signal correctly More attractive in both cell middle and edge deployments Rely on full decoding at the relay, hence cannot achieve full diversity Fall 2011 University of Maryland, ENTS, Adv. Wireless Networks

Implementation Strategies One-way relays Two-way relays Shared relays Fall 2011 University of Maryland, ENTS, Adv. Wireless Networks

Two Way Relay University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Shared Relaying University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

TDD and FDD Relaying TDD relaying suffers from link budget limitation because only a single node transmits at a given time. In FDD relaying, two nodes can transmit simultaneously but the scheme does not allow power and resource sharing between eNB-Relay and Relay-UE links. Fall 2011 University of Maryland, ENTs, Adv. Wireless Networks

Fixed versus Mobile/Movable (Terminal) Relaying   Fixed versus Mobile/Movable (Terminal) Relaying Relaying through Mobile Station In a cellular network with mobile relay station, the nonactive MS (i.e. in idle state) are potential candidate to relay the traffic of the active MS to the BS. PICTURE Fall 2011 University of Maryland, ENTS, Adv. Wireless Networks

Benefits: Low deployment/maintenance cost, since other user’s terminals can potentially act as relays The MS are able to organize themselves in order to cover some unknown dead spots, which are difficult to predict with the operators planning tool They can also be used where it is not cost effective to install FRS such as mountainous environment or subway train platform. They can also be used at unpredictable places like accidents or at infrequently occurring events like demonstrations or sports event If there are a large number of idles MS, there are more choice to select a MRS that can optimize the system performance. For example, a relayed user can choose a MRS with whom it experiences a LOS link. University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Limitations Relaying opportunity depends strongly on the user’s density Relaying through other users terminals can considerably decrease the battery life of the mobile relay station The relaying system performance is highly dependent of the RS selection scheme The signaling (new channel MS-RS, inter-relay handover, RS selection) required for the relaying system might increase considerably The cost of the terminal to support relaying (hardware and software) will increase - the implementations at the hardware become even more difficult if a MRS needs to relay more than one MS’s traffic at the same time. Due to the mobility of the relayed MS and the MRS, frequent inter-relay handoffs might occurs, which might increase the signaling and affect the relaying system performance. Some others issues such as fast fading, power control or security need more investigations in order to make possible the communication between MSs. Fall 2011 University of Maryland, ENTS, Adv. Wireless Networks

Fixed Station Relay : Fixed station relay (FRS) are the low cost station placed at specific location. FRS are part of the network infrastructure, therefore their deployment will be an integral part of the network planning, design and deployment process. Fall 2011 University of Maryland, ENTS, Adv. Wireless Networks

Benefits Operators will have better control of coverage and capacity expected in a specific area The FRS can be deployed at strategic locations in order to maintain a LOS with the BS. They can also use directional antenna to improve the propagation link with the BS The FRSs are less constrained by energy consumption. They may potentially be equipped with more advanced hardware, which enable them to operate in any frequency band as well as allow them to relay several MS at a time. The use of FRS eases the problem of RS selection since fewer number of FRS are deployed compared to MRS. Therefore the signaling overhead required for the RS selection will not be a major issue when relaying with FRS. The inter-relay handoffs will occur only when the relayed MS will move from one FRS to another FRS. Due to their sophisticated hardware, it is more secure to relay through a FRS than MRS. The data are always transferred through a known (fixed) RS University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Limitations : Which one is a better approach ???? Infrastructure’s cost The dimensioning, planning, optimization and maintenance of the FRS can be expensive and cost inefficient Furthermore it might be cost ineffective to install FRS if there are many sparse coverage holes, in which only a few mobile terminals are located Which one is a better approach ???? University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Which one is a better approach ? Although, it has been observed that under certain conditions the uplink capacity gain of 35% is readily achievable for both form of relay stations. But relaying with MRS is a more challenging network than FRS. Thus before a relaying system with MRS can be realized, many issues need to be investigated like : allowing the MRS’s battery to be used for someone else’s call increase of the signaling overhead additional hardware and software will increase the terminal’s cost frequent inter-relay handoffs. University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Pairing Scheme for Relays Selection Centralized relay pairing Distributed relay pairing In this scheme the BS will act as a control node and collects the channel and location information from all the RNs and SS and then make the pairing decision. This information must be formed as a service set and periodically updated in the local BS to capture dynamic changes of SSs This scheme requires more signaling over head, and can achieve better performance gains. In this scheme, RS collects the channel and location information from all the nearby SSs and then makes the pairing decision. First each RS identify its service set of neighborhood SSs and also the channel conditions between its BS as well as its SS, those RS with single service set each randomly selects a time slot from the N- slots in the pairing scheme. If multiple RS choose the same time slot then collusion occurs and those RS will be trying again in the next pairing scheme. University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Handover in Relay Enhanced LTE Network Centralized Relaying Handover: Source Relay Node and Target Relay Node added to the existing network elements Handover initiated by the source eNBr. The source eNBr controls the source RN and the target eNBr controls the target RN The UE is connected to the source eNBr via the source RN Measurement reports are sent to the source eNBr to make the decision. Decision depends upon the UE’s measurements whether a handover must be done or not Handover request is then sent over to the target eNBr, which checks whether an admission of the UE is made with the target RN An acknowledgement is sent to the source eNBr and subsequently to the source RN Any buffered downlink packets must be allocated to the target RN via the target eNBr by the source eNBr Hence, synchronization between the UE and the target RN is established and information regarding Timing Advance for the UE is sent on the uplink The handover is confirmed by the UE to the target RN and the target RN confirms the handover to target eNBr which in turn passes the information to the Gateway via the MME The centralized relaying suggests that the overall process is controlled by the eNBrs (both source and target) Fall 2011 University of Maryland, ENTS, Adv. Wireless Networks

Centralized Handover Fall 2011 University of Maryland, ENTS, Adv. Wireless Networks

Handover in Relay Enhanced LTE Network Distributed/Decentralized Relaying Source RN initiates the handover. Both the RN and eNBr’s work in collaboration to successfully conduct the handover Target eNBr performs the admission control on the backhaul link. The target RN receives the handover request from the target eNBr which then performs the admission control for the relay link Handover request is acknowledged and the handover command is sent to the UE. The downlink data is sent to the target RN through the target eNBr All downlink packets are buffered at the target RN and synchronization is established with the UE. Timing Advance for the UE is performed at the uplink and the handover confirmation message is given to the target RN by the UE The target RN sends the confirmation message to the target eNBr which then sends the handover complete message to the Gateway via the MME The target eNBr receives an acknowledgement from the Serving Gateway. The target eNBr asks the source eNBr to release resources which in turn sends a command to the source RN, which initiated the handover to release resources of the UE The data transfer now takes place between the target RN and the UE after the handover has taken place Fall 2011 University of Maryland, ENTS, Adv. Wireless Networks

Decentralized/Distributed Handover Fall 2011 University of Maryland, ENTS, Adv. Wireless Networks

Relays: Deployment Challenges Uncoordinated Deployment leads to Increase in overall interference in the system Reduce signal to noise ratio(SINR) Lack of good models for relaying in cellular system Routing and resource management Delay and Overhead Increasing number of hops in the system introduces complexity and delay University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Advanced Interference Management Advanced Interference Management techniques such as resource coordination are needed to realize full benefits of heterogeneous deployments. Inter-cell Interference Coordination (ICIC) Interfering base stations can coordinate on transmission powers and/or spatial beams with each other in order to enable control and data transmissions to their corresponding user terminals. Slowly-Adaptive Interference The goal of the slowly-adaptive resource coordination algorithm is to find a combination of transmit powers for all the transmitting base stations and user terminals — and over all the time and/or frequency resources that maximizes the total utility of the network. University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Economic Benefits Lower Capex and Opex cost Wireless backhaul Lower site acquisition cost Less costly antenna structure Faster deployment University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Improve ROI High grade of service Low incremental cost Compatible with GSM, WiMAX and CDMA technologies. Support current and future services(LTE, IMS) Since consumer is always “on” therefore better service and lower churn rate. University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Cost Analysis of Relay vs BS Case Scenarios Heavy Traffic, Urban Deployment Light Traffic, Rural, Suburban Deployment University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Capex and Opex of Relay vs BS (Heavy Traffic, Urban Environment) Normalized w.r.t to 1st Bar University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Capex and Opex of Relay vs BS (Light Traffic, Rural, Suburban Environment) Normalized w.r.t to 1st Bar Number of Relay University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Study Conclusions Conventional Base Station Relay Capex is a significant cost relative to Opex Relay Capex grows with decreasing BS : Relay ratio Capex only slightly larger than Opex under light load Capex considerably less than Opex under heavy load University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

References www.qualcomm.com/.../lte-advanced-heterogeneous-networks.pdf LTE Advanced - Stanford Networking Seminar Heterogeneous Networks - Prof. Robert W. Heath Jr. www.radio-electronics.com › Cellular telecoms www.hindawi.com/journals/wcn/2009/618787/ 202.194.20.8/proc/VTC09Spring/DATA/09-07-03.PDF University of Maryland, ENTS, Adv. Wireless Networks Fall 2011

Thanks University of Maryland, ENTS, Adv. Wireless Networks Fall 2011