Network planning and testing for LTE-Advanced
Simultaneously, various carriers are conducting trials and looking to introduce LTE-Advanced to the masses in 2013, which promises to make a performance leap by bringing more low-powered nodes closer to the user. However, issues around standards and how each carrier will make network handovers complicate things when deploying heterogeneous network components such, as smaller cell sites (e.g., picocells, femtocells, etc.).
LTE-Advanced (LTE-A) is a 3rd Generation Partnership Project (3GPP) specification in response to International Telecommunication Union (ITU) requirements for International Mobile Telecommunications-Advanced (IMT-Advanced) systems. These requirements define what fully compliant 4th generation cell phone mobile communications system needs to satisfy, most importantly:
• Peak speed requirements at 100 Mb/s for high mobility communication (such as from trains and cars) and;
• Peak speed requirements at 1 Gb/s for low mobility communication (such as pedestrians and stationary users).
Even though Mobile WiMAX and LTE don’t meet these objectives, they are considered “4G” technologies since they are significantly better performing and capable then initial 3rd generation systems and are early versions of fully IMT-Advance compliant Mobile WiMAX Release 2 and LTE-Advanced.
For the LTE-Advanced system, 3GPP has further required the following:
• Higher spectral efficiency (from a maximum of 16 bps/Hz in LTE to 30 bps/Hz in LTE-A);
• Improved performance at cell edges (e.g. for downlink 2x2 MIMO at least 2.40 bps/Hz/cell).
What is new in LTE-A
To meet these requirements, LTE-A systems have some improvements compared to LTE, namely, carrier aggregation (CA), improved multi-antenna techniques and support for relay nodes (RN). We will look at each one.
LTE-A systems need considerably more signal bandwidth to meet the requirement of the significant throughput increase compared to 3G and LTE. Since LTE-A also needs to maintain backward compatibility with the LTE terminals, the LTE-A bandwidth increase is performed by aggregating multiple LTE carriers into a single LTE-A signal. Each LTE carrier that comprises the LTE-A signal is called component carrier (CC). A single LTE-A signal can consist of component carriers with different bandwidths as defined in the LTE specification. This allows for effective utilization of the available spectrum.
LTE terminals utilize only one of these carriers while the LTE-A terminals can utilize up to five CC. Per the LTE specification, the maximum bandwidth of a single CC is 20 MHz. Therefore, the maximum LTE-A bandwidth achievable when aggregating five CCs is 100 MHz. It is also important to note that the downlink (DL) and uplink (UL) do not need to be symmetrical, and the downlink can have the same number or more CCs than in the uplink transmission direction. This again allows for effective utilization of the available spectrum, and optimization of the channel based on the throughput required by the user, which is often also asymmetrical.
Improved multi-antenna techniques
To meet the requirement of increased spectral efficiency (throughput per bandwidth), LTE-A had to build on LTE multi-antenna techniques. In high signal-to-noise environments, LTE uses a spatial multiplexing technique called multiple input multiple output (MIMO). MIMO allows higher throughput communication by using two or more transmit (Tx) streams received (Rx) by two or more antennas at the same time while occupying the same bandwidth. Each transmit antenna uses a different reference signal which allows separation of the signals by the receiver. If these antennas are appropriately spaced on the tower and on the terminal, then propagation paths between the transmitting and receiving antennas can be spatially sufficiently different to provide higher throughput with same time/frequency resources.
LTE-A increases the maximum number of the DL antennas from four present in LTE to eight and the maximum number of the UL antennas from the two present in LTE to four. This results in almost double the spectral efficiency in high signal-to-noise environments.
>>Support for Relay Nodes