In 2004, Third Generation Partnership Project (3GPP) industry consortium started to work on fourth-generation (4G) systems. It was predicted at that time that the data rates and spectral efficiencies of WCDMA would not meet the demand of future applications; therefore, a new system had to be developed. The new standard is known as 3GPP Long-Term Evolution, or simply LTE evolved by changing both the air interface and the core network. The air interface used is Orthogonal Frequency Division Multiplexing (OFDM) as modulation, and Orthogonal Frequency Division Multiple Access (OFDMA), with (limited) support for Multiple Input Multiple Output system (MIMO) antenna technology. The core network is evolved into a pure packet switched network. LTE, the next step forward in cellular 3G services provides an uplink speed of up to 50 megabits per second (Mbps) and a downlink speed of up to 100 Mbps. Bandwidth is scalable from 1.25 MHz to 20 MHz. This suits the needs of different network operators that have different bandwidth allocations, and also allows operators to provide different services based on spectrum. LTE improves spectral efficiency in 3G networks, allowing carriers to provide more data and voice services over a given bandwidth.

LTE Design Goals

Due to the wide range of applications and requirements, LTE defines a number of different types of Mobile Stations (MSs) that present a tradeoff between complexity and performance.

The LTE Physical layer (PHY) is designed to meet the following goals:

1) Support scalable bandwidths of 1.25, 2.5, 5.0, 10.0 and 20.0 MHz

2) Peak data rate that scales with system bandwidth

$\quad$ a. Downlink (2 Channel MIMO) peak rate of 100 Mbps in 20 MHz channel

$\quad$ b. Uplink (single Channel Tx) peak rate of 50 Mbps in 20 MHz channel

3) Supported antenna configurations

$\quad$ a. Downlink: 4x2, 2x2, 1x2, 1x1

$\quad$ b. Uplink: 1x2, 1x1

4) Spectrum efficiency

$\quad$ a. Downlink: 5bits/sec/Hz

$\quad$ b. Uplink: 2.5bits/sec/Hz

5) Latency

$\quad$ a. Control - plane: $\lt$ 50 – 100 msec (Control plane refers to all functions and processes that carries signaling traffic, determines the path to use i.e. routing protocols.)

$\quad$ b. User - plane: $\lt$ 10 msec from UE to server (User plane is also known as data plane, carrier plane, forwarding plane or bearer plane, it refers to all functions and processes that carries or forwards the network data or traffic.)

Control-plane latency: It is defined as the time for a handset for transition from various non active states to active states. These are between 50 and 100 ms, depending on the state in which the MS originally was. Furthermore, at least 400 active users per cell should be supported.

User-plane latency: It is defined as the time it takes to transmit a small Internet Protocol (IP) packet to the edge node of the Radio Access Network, RAN. It should not exceed 5 ms in network with a single MS (i.e., no congestion problems).

6) Mobility

$\quad$ a. Optimized for low speeds ($\lt$15 km/hr)

$\quad$ b. High performance at speeds up to 120 km/hr

$\quad$ c. Maintain link at speeds up to 350 km/hr

7) Coverage

$\quad$ a. Full performance up to 5 km

$\quad$ b. Slight degradation 5 km – 30 km

$\quad$ c. Operation up to 100 km should not be precluded by stand