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LTE Telecommunication Primer - Part 2


Fundamental of the LTE (long-term evolution) system, which is my note for a related video on Youtube. This is the second part. MIMO technology and carrier aggregation technique.

Video 8 - MIMO Techniques


This part is the note for the 8th video in the playlist.

Portal: the post of Part 1.


Spatial Diversity

The same message is transmitted in different time slots.

Same message is transmitted at different frequencies.

It uses separate antennas, which are located in different positions to take advantage of the different radio paths, that exist in a typical terrestrial environment. This is the foundation of MIMO.

MIMO Technology

Multiple inputs and multiple outputs. Capacity and coverge enhancement.

Degradation due to multipath propagation decrease link capacity and link reliability. This is addressed by adding more independent fading channels.

Term: diversity gain = # of Tx Antenna x # of Rx Antenna

For example, if we have multiple Rx antenna, we receive multiple copies of the data, thus we can recover original information and increase the robustness.

Shannon’s channel capacity theorem

Capacity (bits/s) = BW x log2(1+SNR)

When using a higher order of modulation scheme, the capacity is increased, meanwhile, the SNR shall be improved to guarantee the fidelity. Therefore it is a trade-off. Sometimes it is difficult, expensive or not compromisable.

Spatial Multiplexing

MIMO in spatial multiplexing

For example, we have two antennae in both Tx and Rx. Then we have information “10101010” to transmit. Then we use T1 antenna to transmit the odd digits and T2 for even digits. The receiving antennas are likewise. Such that we have increased data rate.

\[ R = H\times T \]


\[ T = H^{-1} \times R \]

where \(R\) is the received data, \(T\) is the transmitted data, \(H\) is channel transfer matrix. \(H_{ij}\) is the channel property.

A considerable amount of signal processing is required at the Rx side.

First of all, Rx estimates the individual channel to find the transfer characteristic, which is the element in \(H\).

There are many combinations: SISO, SIMO, MISO, MIMO. Each of them has its advantages and disadvantages.

Beamforming Technology

Use predefined antenna pattern. Transmit the data using the antenna facing the device.

It leverages real-time beamforming, focusing on the direction of the device. We have infinite number of choices in this case.

In Massive MIMO system, eNB has more than 100 antennae. It is popular because it increases data rate (throughput)), SNR and hardens the channel.

Antenna design rule of thumb: the adjacent antenna is separated by \(\frac{\lambda}{2}\) (physically), where \(\lambda\) is the wavelength of the signal. This can be achieved by

Video 9 - Carrier Aggregation Technique

Video Link: LTE - 9

MIMO and OFDM are two cornerstones of the modern wireless communication system. Besides these two, there are

Video 9 focus on carrier aggregation (CA).

Analog to building more traffic lanes to increase throughput, CA is employed to increase bit rate demand.

Component carrier (CC) is achieved by aggregating separate spectrum. The maximum bandwidth supported by LTE is 20 MHz. When we aggregate 5 CC, the maximum aggregated bandwidth is 100 MHz.

CA can be applied to both FDD and TDD. In FDD, DL >= UL, while in TDD, DL = UL.

The cells providing CC is called “serving cell”. Although we have multiple serving cells, there is only one primary cell, who handles the RRC connection. SIB broadcast message is sent to the mobile device, and then mobile device sends the uplink control information back to the primary cell (PCC). The other serving cells are called “secondary cell” (SCC). SCC is added or removed as required, while the PCC is changed at handover.

Intra Band Contiguous

Take Band 40 as an example. The 2.4GHz spectrum is from 2300 MHz to 2360 MHz, it is divided into 3 sections: [2300, 2320], [2320, 2340], [2340, 2360]. Intra band contiguous is the two sections that cover half of each section above: [2310, 2330], [2330, 2350].

Intra band contiguous is the simplest CA deployment. It aggregates multiple adjacent component carriers in a single operation band.

Intro band non contiguous

In practical (in many countries), the spectrum is more fragmented, the contiguous aggregation within the same frequency band may not be possible. There is no intra band contiguous in some cases.

Inter band CA

Different frequency Bands are aggregated. For example, Band 40, Band 3 and Band 5.

CA Configuration

Some terminologies:

CA configuration is eUTRA band + bandwidth classes. For example,

Deploy CA products

CA advantages and disadvantages

From UE’s perspective:

From cell’s perspective:

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