a) Call procedure in GSM :

• First, the subscriber unit must be synchronized to a nearby base station as it monitors the BCH.
• By receiving the FCCH, SCH, and BCCH messages, the subscriber would be locked on to the system and the appropriate BCH.
• To originate a call, the user first dials the intended digit combination and presses the "send" button on the GSM phone.
• The mobile transmits a burst of RACH data, using the same ARFCN as the base station to which it is locked.
• The base station then responds With an AGCH message on the CCCH which assigns the mobile unit to a new channel for SDCCH connection.
• The subscriber unit, which is monitoring TS 0 of the BCH, would receive its ARFCN and TS assignment from the AGCH and would immediately tune to the new ARFCN and TS.
• This new ARFCN and TS assignment is physically the SDCCH {not the TCH).
• Once tuned to the SDCCH, the subscriber unit first waits for the SACCH frame to be transmitted (the wait would last, at most, 26 frames or 120ms), which informs the mobile of any required timing advance and transmitter power command.
• The base station is able to determine the proper timing advance and signal level from the mobile's earlier RACH transmission and sends the proper value over the SACCH for the mobile to process.
• Upon receiving and processing the timing advance information in the SACCH, the subscriber is now able to transmit normal burst messages as required for speech traffic.
• The SDCCH sends messages between the mobile unit and the base station, taking care of authentication and user validation, while the PSTN connects the dialled party to the MSC, and the MSC switches the speech path to the serving base station.
• After a few seconds, the mobile unit is commanded by the base station via the SDCCH to retune to a new ARFCN and new TS for the TCH assignment.
• Once retuned to the TCH, speech data is transferred on both the forward and reverse links, the call is successfully underway, and the SDCCH is vacated.
• When calls are originated from the PSTN, the process is quite similar. The base station broadcasts a PCH message during TS0 within an appropriate frame on the BCH.
• The mobile station, locked on to that same ARFCN, detects its page and replies With an RACH message acknowledging receipt of the page.
• The base station then uses the AGCH on the CCCH to assign the mobile unit to a new physical channel for connection to the SDCCH and SACCH while the network and the serving base station are connected.
• Once the subscriber establishes timing advance and authentication on the SDCCH, the base station issues a new physical channel assignment over the SDCCH and the TCH assignment are made.

b) EDGE architecture:

Edge architecture is a distributed computing architecture that encompasses all the active components in edge computing including all the devices, sensors, servers, clouds, etc. wherever data is processed or used.

GSM EDGE cellular technology is an upgrade to the existing GSM / GPRS networks, and can often be implemented as a software upgrade to existing GSM / GPRS networks. GSM EDGE evolution can provide data rates of up to 384 kbps, and this means that it offers a significantly higher data rate than GPRS.

The GSM EDGE technology requires a number of new elements to be added to the system they are:

- Use of 8PSK modulation:

In order to achieve the higher data rates within GSM EDGE, the modulation format can be changed from GMSK to 8PSK. This provides a significant advantage in being able to convey 3 bits per symbol, thereby increasing the maximum data rate. This upgrade requires a change to the base station. Sometimes hardware upgrades may be required, although it is often simply a software change.

• Base station:

Apart from the upgrade to incorporate the 8PSK modulation capability, other small changes are required to the base station. These are normally relatively small and can often be accomplished by software upgrades.

• Upgrade to network architecture:

GSM EDGE provides the capability for IP based data transfer. As a result, additional network elements are required. These are the same as those needed for GPRS and later for UMTS. In this way the introduction of EDGE technology is part of the overall migration path from GSM to UMTS.

The main network architecture entities that are needed for the EDGE upgrade are:

• SGSN: GPRS Support Node - this forms a gateway to the services within the network.

• GGSN: Gateway GPRS Support Node which forms the gateway to the outside world.

• PCU: Packet Control Unit which differentiates whether data is to be routed to the packet switched or circuit switched networks.

Fig: EDGE Architecture Diagram:

• SGSN: SGSN Support Node element of the GPRS network provides a number of takes focussed on the IP elements of the overall system. It provides a variety of services to the mobiles:

• Packet routing and transfer

• Mobility management

• Authentication

• Attach/detach

• Logical link management

• Charging data

There is a location register within the SGSN and this stores location information . It also stores the user profiles for all the GPRS users registered with the particular SGSN.

• GGSN: GGSN, Gateway GPRS Support Node is one of the most important entities within the GSM EDGE network architecture. The GGSN can be considered to be a combination of a gateway, router and firewall as it hides the internal network to the outside. In operation, when the GGSN receives data addressed to a specific user, it checks if the user is active, then forwarding the data. In the opposite direction, packet data from the mobile is routed to the right destination network by the GGSN.

• PCU: PCU is a hardware router that is added to the BSC. It differentiates data destined for the standard GSM network (circuit switched data) and data destined for the EDGE network (Packet Switched Data). The PCU itself may be a separate physical entity, or more often these days it is incorporated into the base station controller.

c) Software Defined Ratio (SDR):

SDR is a radio communication system that employs reconfigurable software-based components for processing and conversion of digital signals. SDR can transmit and receive signals at different frequencies to implement wireless standards from FM radio to Wi-Fi and LTE.

Fig:Software Defined Ratio:

As shown in Figure above, a typical SDR system consists of an analog front-end and a digital back-end. The analog front-end handles the transmit (Tx) and receive (Rx) functions of a radio communication system. The highest bandwidth SDR platforms are designed to operate over a broad range of frequencies; usually near DC-18 GHz. The front-end of an SDR system handles signals in the analog domain, the back-end processes signals in the digital domain.

The architecture of a typical SDR platform consists of the following boards: power, digital, time, receive (Rx) and transmit (Tx) modules. The boards are connected using high speed cables to ensure fast transfer of data from one board to another. The function of the power board is to supply power to the daughter boards of an SDR system.

Fig:Receive (Rx) and transmit (Tx) chains of an SDR system:

Receive (Rx) board of an SDR platform consists of multiple independent receive channels. Each receive channel is capable of performing the receive functions and handles signals in the analog domain. Analog signals from the Rx board are channeled to an independent chain consisting of amplifiers, down converters, various filters and an ADC for conversion to digital domain. Like the receive (Rx) board, the transmit (Tx) board features multiple independent transmit channels. Each Tx channel is capable of performing transmit functions and sends signals in analog format from the DAC, up converter, filter and amplification stages.