gilat cellular backhaul

Cellular Backhaul Technology

This document contains information proprietary to Gilat Satellite Networks Ltd. and may not be reproduced in whole or in part without the express written consent of Gilat Satellite Networks Ltd. The disclosure by Gilat Satellite Networks Ltd. of information contained herein does not constitute any license or authorization to use or disclose the information, ideas or concepts presented. The contents of this document are subject to change without prior notice

Gilat Network Systems

30/03/2009

[] Cellular Backhaul Technology

2 Proprietary and Confidential

1. Introduction

Widespread popular demand for mobile services such as GSM, CDMA, UMTS and TETRA is increasingly motivating mobile operators to extend wireless services to small, isolated and remote communities as well as to provide mobile services during emergencies and in extreme conditions . Considering that most of these areas are beyond the reach of terrestrial infrastructure, satellite has become a preferred backhaul solution in these circumstances.

Gilat's superior satellite technology provides an end-to-end solution that reduces the capital expenditures (CAPEX) and operational costs (OPEX) incurred by operators by up to 50% making satellite backhaul a profitable and efficient solution.

Gilat’s range of cellular backhaul solutions can handle sites with traffic ranging between a single TRX to virtually unlimited number of TRXs. For very large deployments, Gilat provides a solution based on SCPC that can provide up to E3 (34Mbps) connectivity. Mid-range sites are usually based on MF-TDMA VSATs with SkyAbis Adapters. For smaller sites Gilat provides a split BSC architecture that includes a remote gateway instead of the SkyAbis Adapter.

Figure 1: Network Overview

A SkyAbis adapter connects to the BTS via the E1 interface enabling full Abis support. The SkyAbis adapter connects to the SkyEdge VSAT over the LAN interface. A similar SkyAbis adapter at the Hub side converts the LAN traffic at the Hub back to E1 physical interface with Abis traffic, thus achieving transparency for Abis all the way from BTS to BSC.



2. Network design and Bandwidth on Demand

Mobile network design is based on designing the network for the peak transmission capacity required. This translates to designing the network for each BTS’s peak site. Peak transmission is a relatively short occurrence and the peak does not always occur at the same time for all sites. In addition, the peak changes from day to day with even seasonal effects. The actual traffic snapshot from a mobile network, and this variability can be clearly seen. When designing satellite transmission based on SCPC, the design needs to be for the peak traffic that is to be supported.

The diagram below shows how in a GSM network in South East Asia the amount of excess satellite transmission capacity designed. The graph displays the amount of deployed capacity versus the maximum traffic ever encountered in the site

It is clear from the diagram above that a large proportion of the satellite capacity was never used. In practice, even the peak traffic is a rare occurrence and most of the time much less capacity was required.

Why is so much excess capacity designed into the network?

The graph on the right shows the voice quality dependent on packet loss rate (%). If there is not enough capacity, all calls are affected (not just a few of the calls), practically the BTS will cease to function and no calls will be possible.



Gilat’s cellular backhaul solution uses Dynamic Allocation Multiple Access (DAMA) to re-use the satellite capacity between sites. The traffic snapshot on the right displays the actual bandwidth allocated for the mobile calls versus the amount of traffic actually transmitted. Gilat’s VSAT technology allocated the bandwidth dynamically ensuring no packet loss and no waste of valuable satellite resources.

This is summarized in the tables below, which show the savings of Gilat’s cellular backhaul solution over standard SCPC, dependent both on the capacity of the sites (TRXs) and numbers of sites (BTSs)

The VSAT transmits and receives the packetized Abis information over the satellite channel supporting Ku, C or extended C band frequencies. The VSAT ’s bandwidth on demand along with the software of the adaptor reduces the throughput required over the inbound and outbound channels by 50% to 60% compared to carrying the payload over traditional point-to-point modems.



3. Split-BSC architecture

For very low traffic sites (1-2 TRX) Gilat’s split-BSC architecture solution optimizes traffic between the Picocells and the hub site. The solution splits the BSC functionality between the RGW (Remote Gateway) embedded in the VSAT IDU and the GGW (Ground Gateway) located at the hub site as shown in the following illustration.

SkyEdge

Hub

IP

IP

Ground GW

(GGW)

E1( A)

IP

SkyEdge II

RGW

SkyEdge II

RGW

SkyEdge II Pro

With embedded

Remote

Gateway

(RGW)

MSC

PicocellPicocell

Picocell

IP

Split BSC

Figure 2: Split BSC architecture

Abis signaling from the remote BTS is carried in an optimized IP based format over the satellite link. The hub GGW function adapts this signaling to standard ‘A’ interface format before sending it to the MSC in 64 Kbits E1/T1 channels. To reduce the amount of data sent over the satellite links, the GGW function either discards or terminates unnecessary signaling traffic from the MSC and BTS, as well as compressing voice over satellite, much of the Abis signaling such as all radio resource management is handled at the RGW.

The Gilat VSAT is connected via an Ethernet port directly to the Pico IP packet BTS. The SkyEdge Hub is connected to the GGW which is connected via standard E1/T1 ports transparently to the MSC.

3.1 Bandwidth savings

The split BSC solution introduces significant bandwidth savings. Zero bits are transferred in idle mode which ensures transmission is only used when a call is made. A voice call uses 6kbps versus 38kbps for a non-optimized solution. On a network wide basis this represents a saving of 90% or more.



3.2 Local Call Connectivity

The split BSC solution also enables a key feature – local call connectivity. For local calls – mobile to mobile calls that are both connected to the same backhaul link, there is no need to actually transmit the traffic via satellite. The remote gateway’s special features enable identifying these local calls and then having them terminated locally. This feature is especially important for emergency response teams, since most of the calls are within the disaster site and only a small portion to the central HQ.

The following diagram illustrates the advantage of Local Call Forwarding compared to standard GSM operation.

4. Cellular Bandwidth Optimization

The communications protocols used by cellular equipment are designed based on the typical links

that were available at the time the cellular transmission standards were written. For example, GSM

radio access equipment is designed for E1 circuits and therefore they transmit a high percentage of

“empty” bytes in order to fill the E1 circuits. When using satellite bandwidth, which is generally more

costly than terrestrial links, it is necessary to use the minimal amount of data. A satellite system used

for backhaul needs to be able to adapt the traffic transmitted by the cellular equipment to be

“satellite-friendly” by suppressing any unnecessary bytes and only transmitting the “information”

bytes.

Gilat’s cellular backhaul solution includes the following mechanisms for optimizing the traffic before

it is transmitted over the satellite link:

Figure 3 - Local Call Forwarding



• Idle channel suppression – In most of the cellular systems deployed today, bytes of data are

transmitted by base stations even if when there are no actual calls. This is because these systems

were designed to transmit over E1/T1 circuits. Gilat’s SkyAbis does not transmit any non -active

voice channels and only transmits real voice calls. This Idle Channel Suppression introduces

significant savings of the bandwidth.

• Silence suppression – In most phone conversations only one of the speakers talks at a time.

Gilat’s SkyAbis can recognize silence, and instead of digitizing and transmitting the silence, it can

instead transmit a short packet indicating silence every few seconds. When the receiving side

gets the silence indication, it generates a constant “background noise” until it receives an

indication that the silence has ended. Assuming that each speaker is silent while the other is

speaking, this method can save up to half of the bandwidth.

• Packetization and statistical multiplexing –Gilat’s SyAbis extracts the relevant voice and signaling

information at the cell site and encapsulates it into packets making it possible to fit the

transmission more neatly into the available satellite bandwidth. This statistical gain increases the

lower the activity ration is.

5. Special events and emergency coverage

Mobile Operators that need to

provide additional coverage and

capacity for special events often

have to conduct timely and

expensive line of sight surveys,

lengthy planning, testing and

integration to offer services in a

relatively small commercial window. In

many cases, the pressure to provide

the additional capacity is to reduce

churn, increase brand awareness and

with minimum overall commercial

benefit. With satellite backhaul an

operator can instantly add capacity virtually

anywhere on new towers within the coverage area with no line of sight surveys or other restrictions.

This reduces the operational burden of setting up for special events but also allows the operator to

deploy the transportable “Cell on Wheels” (COW) at short notice where services have been

interrupted or in the event of a major outage such as natural disasters.

One of the common solutions for Emergency response teams is TETRA solution. TETRA enables

private and secure mobile communications. Gilat’s SkyAbis solution provides efficient backhaul for

TETRA networks thus enabling quick response teams to deploy their command post while

maintaining communications with the main HQ.



6. The SkyEdge II System

SkyEdge II is a high performance, high efficiency two-way satellite communication solution used for a variety of applications and services. It combines reliable support for IP communication as well as telephony and multimedia applications utilizing advanced technologies for efficient usage of the satellite’s space-segment resources. SkyEdge II is the optimized solution for every satellite networking need, easily built, maintained and then expanded as the networks requirements change. Offering more than mere connectivity, optional value added services are enabled by add-ons and equipment from Gilat which is integrated with the SkyEdge II system. SkyEdge II is based on the concept of a single hub which can efficiently work with different types of VSATs to support different needs and applications.

.

Figure 4: The SkyEdge II Family of VSATs

The SkyEdge II System is a comprehensive solution for satellite networking. Key benefits of SkyEdge II

are:

High performance for data and multimedia traffic:

o High bit rates in both forward and return link, with up to 135Mbps per outbound

carrier and 6Mbps per inbound carrier

o Comprehensive application acceleration solutions embedded in the VSATs hardware

o Advanced built in QoS mechanisms, allowing high flexibility in meeting user

requirements per the required SLAs and the applications used

Lowest Total Cost of Ownership (TCO) with efficient bandwidth handling:

o High order modulations with Turbo coding on both the inbound and outbound:

o Outbound – 32APSK, 16APSK, 8PSK, QPSK

o Inbound – QPSK, 8PSK



o Dynamic optimization of bandwidth efficiency through the use of Adaptive Coding

and Modulation (ACM) for both the inbound and outbound

o Acceleration, optimization and compression for TCP and HTTP traffic.

o Shared inbound bandwidth for mesh and star traffic

Based on standard technologies

o DVB-S2 outbound

o DVB-RCS inbound

High system reliability

o Highest MTBF for hub and VSAT equipment

o Powerful redundancy schemes for all hub components

o Robust access schemes with adaptive technology in both the inbound and outbound

gilat cellular backhaul

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