Tuesday, 23 December 2014

AAS

An active antenna is an antenna that contains active electronic components.remote radio head (RRH) or antenna-integrated radio designs place the Rf module next to the passive antenna to reduce cable losses

It is to reduce network cost and increase network efficiency. It’s a smart antenna and beam is driven by software.

Active Antenna does not need to be merely passive elements. With intelligent integration, active antenna technology transforms traditional antenna to contribute to base station efficiency. This enables operators to significantly increase the capacity and coverage targets set for their network.

Active Antennas are highly flexible and can meet the needs of many scenarios. They also support rising feature complexity including higher-order MIMO and receiver diversity, while retaining a simple and compact form factor.

Carrier-specific tilting
System-specific tilting
Multi-operator network sharing
Boosting performance with SON
Lower overall site costs
Improved network availability
Higher energy efficiency and RF performance
Reduced network evolution costs

The benefits to be gained include boosted capacity and coverage, higher energy efficiency, lower site rental fees, lower wind loading and reduced investments as new radio technologies come on line and additional spectrum bands become available. As a result,active antenna systems enable operators to not only cut site costs substantially, but to also more cost effectively meet the dynamic demands of their mobile customers.

It is clear that active antenna systems will bring about a step-change in the evolution of radio networks.
This radical new architecture helps operators to cost-effectively address unpredictable demand by creating networks that adapt instantly to changing customer needs, using existing capital investments more efficiently and generating entirely new revenue opportunities. It does this by unleashing frozen network capacity into a reservoir of resources that can flow to fulfil demand, wherever and whenever broadband is used.

AAS BENEFITS

The benefits of active antenna architecture over RRH based site architecture are many.

There is a potential to significantly reduce the site footprint.
The distribution of radio functions within the antenna results in built-in redundancy and improved thermal performance, which can result in higher system availability (lower failure rates).
Distributed transceivers can support a host of advanced electronic beam-tilt features that can enable improvements in network capacity and coverage; hence, it has the potential to lower capital and operational costs.

Antenna RF Diplexer

The antenna diplexer or RF diplexer splitter / combiner used for combining and splitting RF feeders so they can be used by multiple transmitters or receivers which could be on different frequencies.

It is a unit that can be used to enable more than one transmitter to operate on a single RF Antenna. Sometimes these units may be called Antenna duplexers.

USE:

Typically an Antenna diplexer would enable transmitters operating of different frequencies to use the same Antenna.
It is used to allow a single Antenna to be used for transmissions on one band of frequencies and reception on another band.
It is used in a cellular base station to allow it to transmit and receive simultaneously.
It enables the same Antenna system to be used while preventing the transmitted signal from reaching the receiver and blocking the input.
It is used by a broadcast station transmitting on several different frequencies at the same time using the same Antenna.
It enables a single Antenna to be used, while preventing the output from one transmitter being fed back into the output of the other.
Small Antenna diplexers may be used in domestic environments to allow several signals to run along a single feeder. In one application this may allow a single feeder to be used for television and VHF FM radio reception, or to allow terrestrial television signals and this from a satellite low noise box (LNB) to pass down the same lead. These RF diplexers are normally relatively low cost as the specifications are not nearly as exacting as those used for professional RF diplexer installations.

Basic Antenna diplexer concepts

There are a number of ways of implementing RF diplexers. They all involve the use of filters. In this way the paths for the different transmitters and receivers can be separated according to the frequency they use. The simplest way to implement a diplexer is to use a low pass and a high pass filter although band-pass filters may be used. In this way the diplexer routes all signals at frequencies below the cut-off frequency of the low pass filter to one port, and all signals above the cut-off frequency of the high pass filter to the other port. Also here is no path from between the two remote connections of the filters. All signals that can pass through the low pass filter in the diplexer will not be able to pass through the high pass filter and vice versa.

A further feature of an RF diplexer is than it enables the impedance seen by the receiver or transmitter to remain constant despite the load connected to the other port. If the filters were not present and the three ports wired in parallel, neither the Antenna nor the two transmitter / receiver ports would see the correct impedance.

RF diplexer filter requirements

Isolation

When designing an Antenna diplexer a number of parameters must be considered. One is the degree of isolation required between the ports labelled for the high and low frequency transmitter / receiver. If the diplexer is to be used purely for receiving, then the requirement for high levels of isolation is not so high. Even comparatively simple filters give enough isolation to ensure each receiver sees the right impedance and the signals are routed to the correct input without any noticeable loss. Even levels of isolation of 10 dB would be adequate for many installations.
For diplexers that are used to split and combine television and VHF FM radio along a single line, the levels of isolation are likely to be very low.

The next case is when the diplexer is to be used for transmitting only. It will be necessary to ensure that the levels of power being transferred back into a second transmitter are small. Power being fed into the output of a transmitter in this way could give rise to intermodulation products that may be radiated and cause interference. It is also important to ensure that the transmitters see the correct impedance, and that the presence of the second transmitter does not affect the impedance seen by the first. Typically levels of isolation between the transmitter ports of 60 - 90 dB may be required.

The final case is where one of the ports is used for transmitting, and the other for receiving simultaneously. In this instance very high levels of isolation are required to ensure that the minimum level of the transmitter power reaches the receiver. If high levels of the transmitter signal reach the receiver, then it will be desensitised preventing proper reception of the required signals. Levels of isolation in excess of 100 dB are normally required for these applications.

Band pass filters

Under some circumstances band pass filters may be used. These may be used where comparatively narrow bandwidth is required for either or both of the transmitter / receiver ports. Sometimes a very high Q resonant circuit may be used. By using this approach high degrees of rejection can be achieved. Often repeater stations which receive on one channel and transmit on another simultaneously use diplexers that utilise this approach.

LTE Throughput Calculation

Solution:

1 RB = 12 sub-carriers

1 Sub-carrier = 7 OFDM symbols in time domain = 7 Resource elements

Thus total OFDM symbols in 1 RB = 12 X 7

With 64 QAM 1 symbol = 6 bits

Thus total bits in 1 RB = 12 X 7 X 6 transmitted in 0.5 msec

With 20 MHZ BW, 100 RB are transmitted

Thus total bits in 100 RB = 12 X 7 X 6 X 100 transmitted in 0.5 msec

Thus in 1 msec, total bits transmitted = 12 X 7 X 6 X 2 X100

In 1 sec, total transmitted bits = 12 X 7 X 6 X 2 X 100 X 1000 = 100.8 Mbps

This is possible with Single antenna configuration

But with 4 x 4 MIMO

Maximum throughout = 4 X 100.8 = 403.2 Mbps

Wednesday, 3 December 2014

LTE Optimisation by Celplan

PART1: What LTE parameters need to be Dimensioned and Optimized

PART2: What LTE parameters need to be Dimensioned and Optimized

Spectrum Analysis for LTE systems

Technical Writing

Pages