Category: Access and Physical Layer

Long Term Evolution (LTE), VOLTE and VOWifi

Both radio and core network evolution
all-IP packet-switched architecture
standardised by 3GPP
lower CAPEX ans OPEX involved

Evolved from Universal Mobile Telecommunication System (UMTS), which in turn evolved from the Global
Also aligned with 4G (fourth-generation mobile)

LTE is backward compatible with GSM/EDGE/UMTS/CDMA/WCDMA systems on existing 2G and 3G spectrum , even hand-over and roaming to existing mobile networks.

    Motivation for evolution

    Wireless/cellular technology standards are constantly evolving for better efficiency and performance.
    LTE evolved as a result of rapid increase of mobile data usage. Applications such as voice over IP (VOIP), streaming multimedia, videoconferencing , cellular modemetc.
    It provides packet-switched traffic with seamless mobility and higher qos than predecessors.
    Also high data rate, throughput, low latency and packet optimized radioaccess technology on flexible bandwidth deployments.

    Performance

    Peak Data Rate
    uplink – 75Mbps(20MHz bandwidth)
    downlink – 150 Mbps(UE Category 4, 2×2 MIMO, 20MHz bandwidth) , 300 Mbps(UE category 5, 4×4 MIMO, 20MHz bandwidth)

    carrier bandwidth can range from 1.4 MHz up to 20 MHz. Ultimately bandwidth used by carrier depends on frequency band and the amount of spectrum available with a network operator
    Mobility 350 km/h

    Multiple Access Schemes
    uplink: SC-FDMA (Single Carrier Frequency Division Multiple Access) 50Mbps+ (20MHz spectrum)
    downlink: OFDM (Orthogonal Frequency Division Multiple Access) 100Mbps+ (20MHz spectrum)

    Multi-Antenna Technology , Multi-user collaborative MIMO for Uplink and TxAA, spatial multiplexing, CDD ,max 4×4 array for downlink

    Coverage 5 – 100km with slight degradation after 30km

    LTE architecture supports hard QoS and guaranteed bit rate (GBR) for radio bearers.

    Technology

    All interfaces between network nodes are IP based
    Duplexing – Time Division Duplex (TDD) , Frequency Division Duplex (FDD) and half duples FD
    (MIMO) Multiple Input Multiple Output transmissions – LTE devices have to support this. Allows the base station to transmit several data streams over the same carrier simultaneously.
    Modulation Schemes QPSK, 16QAM, 64QAM(optional)

    LTE Architecture

    Primarily composed of

    1. User Equipment (UE)
    2. Evolved UMTS Terrestrial Radio Access Network (E-UTRAN).
    3. Evolved Packet Core (EPC).

    LTE-Advanced

    LTE devices capable of CAT6 speeds (Category 6 )
    Increased peak data rate, downlink 3 Gbps, Uplink 1.5 Gbps ( 1 Gbps = 1000 Mbps)
    spectral efficiency from 16bps/Hz in R8 to 30 bps/Hz in R10
    Carrier Aggregation (CA)
    enhanced use of multi-antenna techniques
    support for Relay Nodes (RN)

    Ref:
    3GPP on LTE – https://www.3gpp.org/technologies/keywords-acronyms/98-lte
    ETSI on LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio transmission and reception – https://www.etsi.org/deliver/etsi_ts/136100_136199/136101/10.03.00_60/ts_136101v100300p.pdf

    MIMO ( multiple-input and multiple-output )

    SISO – Single Input Single Output
    SIMO – Single Input Multiple output
    MISO – Multiple Input Single Output
    MIMO – Multiple Input multiple Output

    Multiplying the capacity of a radio link using multiple transmission and receiving antennas to exploit multipath propagation.
    Key technology for achieving a vast increase of wireless communication capacity over a finite electromagnetic spectrum.

    Antenna configuration – implies antenna spatial diversity by useing arrays of multiple antennas on one or both ends of a wireless communication link
    boost channel capacity.
    combats multipath fading
    enhance signal to noise ratio,
    create multiple communication paths

    Applies to wifi
    IEEE 802.11n (Wi-Fi), IEEE 802.11ac (Wi-Fi)
    as well as cellular networks
    HSPA+ (3G)
    WiMAX (4G)
    Long Term Evolution (4G LTE)
    power-line communication for 3-wire installations as part of ITU G.hn standard and HomePlug AV2 specification

    Large capacity increases over given bandwidth and S/N resources
    Greater throughputs on bands below 6 GHz,

    multi-user MU-MIMO

    simultaneous independent data links to multiple users over a common time-frequency resource

    massive MIMO

    enable the expansion of the useful spectrum to microwave and millimeter wave bands within the framework of 5G cellular communication.

    microdiversity MIMO

    MIMO modes (60m)

    Diversity – Alamouti algorithm
    Beam forming – create and aim the antenna pattern electronically
    Spatial multiplex – use of precoding and shaping to unravel the multipath signals

    challenges faced by mobile equipment vendors implementing MIMO in small portable devices.

    Functions

    3main categories: precoding, spatial multiplexing (SM), and diversity coding.

    Precoding

    multi-stream beamforming ( signal is emitted from each of the transmit antennas with appropriate phase and gain weighting such that the signal power is maximized at the receiver input ) , increases reception and reduce multipath fading

    In line-of-sight propagation, beamforming results in a well-defined directional pattern. However, conventional beams are not a good analogy in cellular networks, which are mainly characterized by multipath propagation. When the receiver has multiple antennas, the transmit beamforming cannot simultaneously maximize the signal level at all of the receive antennas, and precoding with multiple streams is often beneficial. Note that precoding requires knowledge of channel state information (CSI) at the transmitter and the receiver.

    Spatial multiplexing

    High-rate signal is split into multiple lower-rate streams and each stream is transmitted from a different transmit antenna in the same frequency channel. If these signals arrive at the receiver antenna array with sufficiently different spatial signatures and the receiver has accurate CSI, it can separate these streams into (almost) parallel channels.

    increasing channel capacity at higher signal-to-noise ratios (SNR).

    Diversity coding

    when there is no channel knowledge at the transmitter , a single stream is transmitted. The signal is emitted from each of the transmit antennas with full or near orthogonal coding. Diversity coding exploits the independent fading in the multiple antenna links to enhance signal diversity.

    Ref :
    https://www.comsoc.org
    https://en.wikipedia.org/wiki/MIMO