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LTE System Overview

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LTE System Overview

Confidential Information of Huawei. No Spreading Without Permission

LTE System Overview

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LTE System Overview

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Mobile networks have been evolving for many years. The initial systems, which are referred to as “First Generation” were launched commercially at the end of the 1980’s. the pressure for greater capacity, more security and roaming saw these replaced with “Second Generation”, and more recently “Third Generation” solutions. Today, the growth in mobile broadband has promoted the development of 4G or “Fourth Generation” systems. 1st Generation mobile systems used analogue modulation techniques. These analogue systems were proprietary, and based on Frequency Modulation. For this reason, they all lacked security, any meaningful data service or international roaming capability. The main commercial systems deployed around the world included AMPS, TACS and ETACS. AMPS The first AMPS system appeared in 1976 in the USA. From its initial commercial p launch it was mainly implemented in the America, Russia and Asia. Various issues including weak security features made the system prone to hacking and handset cloning. TACS The European version of AMPS but with slight modifications including its operation p on different frequency bands. It was mainly used in the UK, as well as part of Asia. ETACS An improved version of TACS. It enabled a greater number of channels and p therefore facilitated more users.

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The development of GSM, GPRS, EDGE, UMTS, HSPA and LTE, as well as the strategy for future mobile networks has been coordinated and planned by the various parties that sit within the 3GPP working groups. This development roadmap is based on a series of specification releases. The diagram shows the key Release milestones. These started with the introduction of GPRS in Release 97 and chart the evolution of 3GPP networks up to the introduction of LTE and beyond. Pre-Release 99 Pre-Release 99 saw the introduction of GSM, as well as the addition of GPRS. The p main GSM Phases and 3GPP Releases include: n

GSM Phase 1.

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GSM Phase 2.

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GSM Phase 2+ (Release 96).

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GSM Phase 2+ (Release 97).

GSM Phase 2+ (Release 98). 3GPP Release 99 3GPP Release 99 saw the introduction of UMTS, as well as the EDGE enhancement p to GPRS. UMTS contains all the features needed to meet the IMT-2000 requirements as those defined by the ITU. It is able to support CS voice and video services, as well as PS data services over common and dedicated bearers. Initial data rates for UMTS were 64kbit/s, 128kbit/s, and 384kbit/s. Note that the theoretical maximum was 2Mbit/s. n

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LTE System Overview

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Heterogeneous Network, or HetNet for short, stands for the different types of base stations (macro, micro, pico, relay) operating on different technologies (GSM, WCDMA and LTE) are used together in the same network to build the good coverage and high capacity, that end-users demand from their operator. This concept is contrary to ‘homogeneous’ networks, HomoNet for short, that are mainly built with one type of base station, often macro. FusionNet Huawei in Barcelona at the Mobile World Congress (MWC 2013) demonstrated the p next generation LTE-B (R12/R13) network architecture FusionNet. It combines multi-system, multi-band, multi-layer heterogeneous networks, improved 500% cell edge user throughput, which really create borderless networks. The core of FusionNet is based on LTE-B techniques (such as multi-flow p aggregation, interference coordination, service adaptation, spectrum efficiency optimization, etc.). With the existing LTE, LTE-A (such as multi-point coordinate, carrier aggregation), FusionNet realizes multi-system, multi-band, multi-layer network of deep integration, to help operators significantly reduce CAPEX and OPEX, allowing users to enjoy ultra-broadband, zero-waiting and ubiquitous connectivity.

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Technical advantages to 3G: High data throughput, PS transmission, lower latency, wider coverage and downward compatibility

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LTE System Overview

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The LTE network has a flat architecture, which has the following characteristics: The RNC is removed from the radio access network. The only NE in the radio p access network is the NodeB. The MSC server and MGW are removed from the core network. Voice services are p provided based on IP. The PS domain of the core network adopted an architecture similar to softswitch. p It separates the control plane from user plane. n

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The mobility management entity (MME) stores UE contexts on the control plane, including the ID, status, and tracking area of the UE. It manages and allocates an ID to an UE. The MME also performs functions such as mobility management, authentication, key management, encryption, and integrity protection. A serving gateway (SGW) provides functions such as paging, information management for a UE in idle state, mobility management, encryption on the user plane, PDCP, SAE bearer control, and encryption and integrity protection for NAS signaling.

It is an all-IP network. The reasons for this design are as follows: Too many network layers make it impossible to meet the requirement for low p delay, which is less than 10 ms on the radio network side. The all-IP network has the lowest costs because the VoIP technology is already p mature. n

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All the interfaces within the EPC, and those extending to functions outside of the EPC, are denoted by the letter “S”. These all use the service of IP. Elements supporting LTE operation, apart from MME, S-GW and PDN-GW, include the HSS, PCRF and ePDG. The RNC and SGSN may also be involved. HSS (Home Subscriber Server) is considered to be a “master” database. Although logically it is considered as one entity, the HSS in practice is made up of several physical databases depending on the number of subscribers and redundancy requirements. The HSS holds variables and identities for the support, establishment and maintenance of calls and sessions made by subscribers. PCRF (Policy and Charging Rules Function) supports functionality for policy control and charging control. As such, it provides bearer network control in terms of QoS and the allocation of the associated charging vectors. ePDG (evolved Packet Data Gateway) is used when connecting to Untrusted Non 3GPP IP Access networks. It provides functionality to allocate IP addresses in addition to encapsulating/ de-capsulating IPSec and PMIP tunnels.

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GUTI =GUMMEI + M-TMSI =(MCC + MNC + MMEI) + M-TMSI =(MCC + MNC + (MMEGI + MMEC)) + M-TMSI =(MCC + MNC + MMEGI) + S-TMSI GUMMEI：Globally Unique MME Identifier MMEI：MME Identifier MMEGI: MME Group Identifier TMSI: Temporary Mobile Subscriber Identity MMEI=MMEGI + MMEC S-TMSI=MMEC + M-TMSI

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The eNB hosts the following functions: Functions for Radio Resource Management: Radio Bearer Control, Radio Admission p Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling); IP header compression and encryption of user data stream; p Selection of an MME at UE attachment when no routing to an MME can be p determined from the information provided by the UE; Routing of User Plane data towards Serving Gateway; p Scheduling and transmission of paging messages (originated from the MME); p Scheduling and transmission of broadcast information (originated from the MME p or O&M); Measurement and measurement reporting configuration for mobility and p scheduling; Scheduling and transmission of PWS (which includes ETWS and CMAS) messages p (originated from the MME).

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Mobility Management Entity (MME): The MME manages mobility, UE identities and security parameters. MME functions includes: NAS signalling; p NAS signalling security; p AS Security control; p Inter CN node signalling for mobility between 3GPP access networks; p Idle mode UE Reachability (including control and execution of paging p retransmission); Tracking Area list management (for UE in idle and active mode); p PDN GW and Serving GW selection; p MME selection for handovers with MME change; p SGSN selection for handovers to 2G or 3G 3GPP access networks; p Roaming; p Authentication; p Bearer management functions including dedicated bearer establishment; p Support for PWS (which includes ETWS and CMAS) message transmission; p Optionally performing paging optimisation. p

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LTE System Overview

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LTE System Overview

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For details about SCTP, see RFC2960. For details about UDP, see RFC 768.

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LTE System Overview

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LTE System Overview

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LTE System Overview

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LTE System Overview

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LTE System Overview

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LTE System Overview

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LTE System Overview

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LTE System Overview

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LTE System Overview

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OFDM has a history of 40 years in application, and it is initially used in radio communications in military. In 1950s, American military established the first multi-carrier modulation system. In 1970s, the OFDM system with massive subcarriers appeared. However, mass commercial application did not appear due to the system complexity and high costs. In 1990s, with the development of digital communication technologies, IFFT on the OFDM transmitter side and FFT on the OFDM receiver side reduces system complexity, enabling OFDM to be widely used.

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LTE System Overview

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LTE System Overview

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In traditional FDMA transmission, a channel is divided into multiple independent subchannels to transmit data streams in parallel, and the sub-channels are separated by a group of filters on the receiver. This method is simple and direct while the spectral efficiency is low because guard-bands are required between sub-channels. However, subcarriers in the OFDM system are overlapping and orthogonal, which greatly improves the spectral efficiency compared with common FDA systems, as shown in the preceding figure. The orthogonal modulation and demodulation in each sub-channel can be performed using IDFT and DFT. For systems with large N value, FFT can be used. IFFT and FFT are easy to perform with the development of large-scale integrated circuit and DSP technologies, as shown in the preceding figure.

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Why CP is needed:

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How CP is added

Integrate (FFT) any 64 samples within the extended period

Base symbol period, e.g 64 samples

Extension, e.g 10 samples

Base symbol period, e.g 64 samples

Extended symbol period, e.g 64+10=74 samples

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Deep fading does not occur simultaneously in all subcarriers due to the frequency selectivity. Therefore, dynamic bit or subcarrier allocation technology can be used to utilize the sub-channels with high SNR and improve the system performance. In a multi-user system, a subcarrier that is in poor performance for a user probably is in good performance for another user. Therefore, a sub-channel is not disabled unless it is in poor performance for all users, which occurs at a low probability. The single-carrier system performs adaptive modulation and coding (AMC) based on the average SINR in the entire system, while the multi-carrier system performs AMC based on the average SINR in different frequency bands.

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Orthogonality is required because spectrums of sub-channels overlap each other. Frequency offset of radio signals, such as Doppler Shift, can be caused by radio channel change with time. In addition, the difference between transmitter carrier frequency and receiver oscillator frequency can also cause frequency offset, destroying the orthogonality of subcarriers in the OFDM system. As a result, intercarrier interference (ICI) among sub-channels is generated, deteriorating the BER of the system. The vulnerability to the frequency offset is the primary disadvantage of the OFDM system.

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Different from single-carrier systems, multi-carrier system outputs combined signals of multiple sub-channels. If these signals are in the same phase, the power of combined signals must be higher than the average power of signals, resulting in a high PAR. To reduce the high PAR, high linearity of the PA in the transmitter is required. If the dynamic range of the PA cannot adjust to the signal change, signals are deformed, changing the spectrum of the combined signals. As a result, the orthogonality of signals in multiple sub-channels is destroyed, leading to interference and deteriorated system performance.

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LTE System Overview

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The multiple-access technology is used to distinguish users in a system, including FDMA, TDMA, and CDMA. FDMA: The first-generation mobile telecommunications uses FDMA, which divides a frequency into multiple channels and is easy to deploy. However, the system capacity is limited due to limited frequency resources. TDMA: Based on FDMA, TDMA divides each frequency in both the frequency domain and time domain, increasing the system capacity and improving the spectral efficiency. CDMA: CDMA distinguishes users based on the frequency, time, and code. In this way, the system capacity is further improved. However, CDMA has a high requirement in interference resistance technology. In terms of capacity, the capacity of a TDMA system is four to six times as large as that of an FDMA system while the capacity of a CDMA system is ten to twenty times as large as that of an FDMA system. The system capacity is closely related to the carrier-to-interference ratio (CIR), which refers to a ratio of the strength of a carrier signal to the strength of an interfering signal in a radio channel. If a large CIR is required, the interference resistance of the system is weak, and the system capacity is small. In terms of deployment, FDMA is the easiest one while CDMA is the most complicated one. Orthogonal Frequency-Division Multiple Access (OFDMA) is a multi-user version of the orthogonal frequency-division multiplexing (OFDM) digital modulation scheme. As shown in the figure, a bandwidth is divided into smaller units, that is, subcarrier. These subcarriers are grouped and allocated to UE. The UE can be allocated with different resources in both the time domain and frequency domain. Confidential Information of Huawei. No Spreading Without Permission

LTE System Overview

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LTE System Overview

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Compared with CDMA, OFDMA has the following advantages: n

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Effectively eliminating multipath interference in radio communications by using cyclic prefixes Achieving orthogonal frequency multiplexing between users with an ensured spectral efficiency Combining OFDM and MIMO Technology

Supporting frequency link adaptation and multi-user scheduling OFDMA is a multiple-access modulation scheme based on resources in the time and frequency domains. The smallest resource in the frequency domain is subcarriers and the smallest unit in the time domain is slot. For scheduling, the smallest unit is RB, which occupies 12 subcarriers in frequency domain, and 1ms in time domain. n

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Compared with OFDMA, SC_FDMA has the following advantages: n

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Lower PAPR, facilitating the design of UE PAs Achieving orthogonal frequency multiplexing between users with an ensured spectral efficiency

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Achieving multiplexing by using DFT and orthogonal subcarrier mapping

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Supporting frequency link adaptation and multi-user scheduling

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The figure shows the SC-FDMA subcarrier mapping concept. The basic transmitter and receiver architecture is very similar (nearly identical) to OFDM, and it offers the same degree of multipath protection. Importantly, because the underlying waveform is essentially a single carrier, the PAPR is lower. In the figure, the SC-FDMA signal generation process starts by creating a time domain waveform of data symbols to be transmitted. This is then converted into the frequency domain, using a DFT (Discrete Fourier Transform). DFT length and sampling rate are chosen so that the signal is fully represented, as well as being spaced 15kHz apart. Each subcarrier will have its own fixed amplitude and phase for the duration of the SC-FDMA symbol. Next the signal is shifted to the desired place in the channel bandwidth using the zero insertion concept, i.e. subcarrier mapping. The signal is then converted to a single carrier waveform using an IDFT (Inverse Discrete Fourier Transform) in addition to other functions. Finally a cyclic prefix can be added. Note that additional functions such as S-P (Serial to Parallel) and P-S (Parallel to Serial) converters are also required as part of a detailed functional description.

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The figure illustrates the concept of the DFT, such that a group of N symbols map to N subcarriers. However depending on the combination of the N symbols into the DFT, the output will vary. As such, the actual amplitude and phase of the N subcarriers is more like a “code word”.

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At the eNodeB, the receiver takes the N subcarriers and reverses the process. This is achieved using an IDFT (Inverse Discrete Fourier Transform) which effectively reproduces the original N symbols. The figure illustrates the basic view of how the subcarriers received at the eNodeB are converted back into the original signals. Note that the SC-FDMA symbols have a constant amplitude and phase, and like OFDMA, a CP is still required.

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LTE System Overview

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LTE System Overview

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LTE System Overview

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LTE System Overview

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LTE System Overview

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LTE System Overview

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LTE System Overview

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Each 10 ms radio frame consists of two half-frames of 5 ms each. Each half-frame consists of eight slots of length 0.5 ms and three special fields: DwPTS, GP and UpPTS (DwPTS+GP+UpPTS=1ms). GP is reserved for downlink to uplink transition. Other Subframes are assigned for either downlink or uplink transmission. Uplink and downlink transmissions are separated in the time domain.

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LTE System Overview

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Df=7.5kHz is available for MBSFN（MBMS over Single Frequency Network），which defined in 3GPP Protocol 8 but applied until 3GPP Protocol9. Attention:7.5kHz is only adapted for downlink.

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RE (Resource Element) Minimum unit in physical resource p Time domain: 1 OFDM Symbol, frequency domain: 1 Subcarrier p RB（Resource Block） Minimum unit for resource allocation used for data transmission in physical lay p Time domain: 1 Slot; frequency domain: 12 continuous subcarriers p CCE(Control Channel Element) Resource unit for control channel p 1 CCE = 36 REs p 1 CCE = 9 REGs (1 REG = 4 REs) p TTI (Transmission Time Interval) Basic unit in time domain when scheduling data in physical lay p 1 TTI = 1 subframe = 2 slots p 1 TTI = 14 OFDM symbols(Normal CP) p 1 TTI = 12 OFDM symbols (Extended CP) p

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LTE System Overview

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