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`LTELTE
`
`LTE (both radio and core network evolution) is now on the market. Release 8 was
`frozen in December 2008 and this has been the basis for the first wave of LTE
`equipment. LTE specifications are very stable, with the added benefit of
`enhancements having been introduced in all subsequent 3GPP Releases.
`
`The motivation for LTE
`
`Need to ensure the continuity of competitiveness of the 3G system for the future
`User demand for higher data rates and quality of service
`Packet Switch optimised system
`Continued demand for cost reduction (CAPEX and OPEX)
`Low complexity
`Avoid unnecessary fragmentation of technologies for paired and unpaired band operation
`
`LTE Overview
`
`Author: Magdalena Nohrborg, for 3GPP
`
`LTE (Long Term Evolution) or the E-UTRAN (Evolved Universal Terrestrial Access Network), introduced in 3GPP R8, is the
`access part of the Evolved Packet System (EPS). The main requirements for the new access network are high spectral
`efficiency, high peak data rates, short round trip time as well as flexibility in frequency and bandwidth.
`
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`Figure 1 Network Solutions from GSM to LTE
`Figure 1 Network Solutions from GSM to LTE
`
`GSM was developed to carry real time services, in a circuit switched manner (blue in figure 1), with data services only possible
`over a circuit switched modem connection, with very low data rates. The first step towards an IP based packet switched (green
`in figure 1) solution was taken with the evolution of GSM to GPRS, using the same air interface and access method, TDMA
`(Time Division Multiple Access).
`
`To reach higher data rates in UMTS (Universal Mobile Terrestrial System) a new access technology WCDMA (Wideband Code
`Division Multiple Access) was developed. The access network in UMTS emulates a circuit switched connection for real time
`services and a packet switched connection for datacom services (black in figure 1). In UMTS the IP address is allocated to the
`UE when a datacom service is established and released when the service is released. Incoming datacom services are therefore
`still relying upon the circuit switched core for paging.
`
`The Evolved Packet System (EPS) is purely IP based. Both real time services and datacom services will be carried by the IP
`protocol. The IP address is allocated when the mobile is switched on and released when switched off.
`The new access solution, LTE, is based on OFDMA (Orthogonal Frequency Division Multiple Access) and in combination with
`higher order modulation (up to 64QAM), large bandwidths (up to 20 MHz) and spatial multiplexing in the downlink (up to 4x4)
`high data rates can be achieved. The highest theoretical peak data rate on the transport channel is 75 Mbpsin the uplink, and in
`
`Exhibit 1028
`IPR2022-00726
`U.S. Patent 8,077,594
`
`

`

`the downlink, using spatial multiplexing, the rate can be as high as 300 Mbps.
`
`The LTE access network is simply a network of base stations, evolved NodeB (eNB), generating a flat architecture (figure 2).
`There is no centralized intelligent controller, and the eNBs are normally inter-connected viathe X2-interface and towards the
`core network by the S1-interface (figure 2). The reason for distributing the intelligence amongst the base-stations in LTE is to
`speed up the connection set-up and reduce the time required for a handover. For an end-user the connection set-up time for a
`real time data session is in many cases crucial, especially in on-line gaming. The time for a handover is essential for real-time
`services where end-users tend to end calls if the handover takes too long.
`
`
`
`Figure 2. X2 and S1 Interfaces
`Figure 2. X2 and S1 Interfaces
`
`Another advantage with the distributed solution is that the MAC protocol layer, which is responsible for scheduling, is
`represented only in the UE and in the base station leading to fast communication and decisions between the eNB and the UE.
`In UMTS the MAC protocol, and scheduling, is located in the controller and when HSDPA was introduced an additional MAC
`sub-layer, responsible for HSPA scheduling was added in the NB.
`
`The scheduler is a key component for the achievement of a fast adjusted and efficiently utilized radio resource. The
`Transmission Time Interval (TTI) is set to only 1 ms.
`
`During each TTI the eNB scheduler shall:
`
`· consider the physical radio environment per UE. The UEs report their perceived radio quality, as an input to the
`scheduler to decide which Modulation and Coding scheme to use. The solution relies on rapid adaptation to channel
`variations, employing HARQ (Hybrid Automatic Repeat Request) with soft-combining and rate adaptation.
`
`· prioritize the QoS service requirements amongst the UEs. LTE supports both delay sensitive real-time services as
`well as datacom services requiring high data peak rates.
`
`· inform the UEs of allocated radio resources. The eNB schedules the UEs both on the downlink and on the uplink. For
`each UE scheduled in a TTI the user data will be carried in a Transport Block (TB). DL there can be a maximum of two
`TBs generated per TTI per UE – if spatial multiplexing is used. The TB is delivered on a transport channel. In LTE the
`number of channels is decreased compare to UMTS. For the user plane there isonly one shared transport channel in each
`direction. The TB sent on the channel, can therefore contain bits from a number of services, multiplexed together.
`
`To achieve high radio spectral efficiency as well as enable efficient scheduling in both time and frequency domain, a multicarrier
`approach for multiple access was chosen by 3GPP. For the downlink, OFDMA (Orthogonal Frequency Division Multiple Access)
`was selected and for the uplink SC-FDMA (Single Carrier - Frequency Division Multiple Access) also known as DFT (Discrete
`Fourier Transform) spread OFDMA (figure 3).
`
`Figure 3 OFDMA and SC-FDMA
`Figure 3 OFDMA and SC-FDMA
`
`

`

`OFDM is a multicarrier technology subdividing the available bandwidth into a multitude of mutual orthogonal narrowband
`subcarriers. In OFDMA these subcarriers can be shared between multiple users. The OFDMA solution leads to high Peak-to-
`Average Power Ratio (PAPR) requiring expensive power amplifiers with high requirements on linearity, increasing the power
`consumption for the sender. This is no problem in the eNB, but would lead to very expensive handsets. Hence a different
`solution was selected for the UL. As illustrated in figure 3, the SC-FDMA solution generates a signal with single carrier
`characteristics, hence with a low PAPR.
`
`To enable possible deployment around the world, supporting as many regulatory requirements as possible, LTE is developed for
`a number of frequency bands – E-UTRA operating bands- currently ranging from 700 MHz up to 2.7GHz. The available
`bandwidths are also flexible starting with 1.4 MHz up to 20 MHz. LTE is developed to support both the time division duplex
`technology (TDD) as well as frequency division duplex (FDD). In R8 there are 15 bands specified for FDD and eight bands for
`TTD. In R9 four bands were added for FDD. Also added in R9 were for example Multimedia Broadcast Multicast Service
`(MBMS), and Home eNB (HeNB), see figure 4. MBMS is used to provide broadcast information to all users, for example
`advertisement, and multicast to a closed group subscribing to a specific service, e.g. streaming TV. HeNBs are introduced
`mainly to provide coverage indoors, in homes or offices.The HeNB is a low power eNB that will be used in small cells – femto
`cells. Normally it will be owned by the customer, deployed without any network planning and connected to the operators EPC
`(Evolved Packet Core).
`
` Figure 4 New in LTE R9: a) MBMS, b) HeNB.
`
`
`
`
`
`
`

`

`Further reading
`
`· TS 36.211 Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation
`
`· TS 36.212 Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding
`
`· TS 36.213 Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures
`
`· TS 36.300 Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network
`(E-UTRAN); Overall description; Stage 2
`
`· TS 36.321 Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC) protocol specification
`
`· TS 36.331 Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification
`
`· TS 36.413 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP)
`
`· TS 36.423 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 Application Protocol (X2AP)
`
`
`
`LTE Historical Information
`
`The technical paper UTRA-UTRAN Long Term Evolution (LTE) and 3GPP System Architecture Evolution (SAE) is a
`good starting point.
`
`Initiated in 2004, the Long Term Evolution (LTE) project focused on enhancing the Universal Terrestrial Radio Access
`(UTRA) and optimizing 3GPP’s radio access architecture.
`
`The 3GPP 36 series of specifications, covers the "Evolved Universal Terrestrial Radio Access (E-UTRA)".
`
`See also - the technologies page on LTE-Advanced, which describes the work beyond LTE Release 8/9.
`
`...Get details of how to use the LTE and LTE-Advanced logos
`
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`
`5G NR (Rel-15)
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`nodes (CUPS)
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