Simulation Of Inmarsat C Channels Using Matlab Computer Science Essay Example

per the latest convention, land-based mobile users can also avail these services globally.

The report discusses software algorithms for the modulators and demodulators of inmarsat C channels. These algorithms are usually advanced and include a fast Fourier transform (FFT)-based burst acquisition algorithm, carrier phase tracker, innovative Doppler tracker, and acquisition symbol synchronizer. They are extensively simulated to ensure reliable burst reception. The demodulator hardware, based on a compact digital signal processor (DSP), utilizes a special personal computer test interface for downloading test data files.

Inmarsat offers global services that adhere to international standards, allowing mobile devices to operate and roam worldwide. However, it is important to strictly adhere to international licensing requirements in applicable regions. This benefits users by providing a global service terminal and reducing operating costs. Additionally, manufacturers can tap into a large market and gain a large user base, leading to reduced production costs for equipment.

The Inmarsat Standards System has introduced technical standards for land mobile communications, leading to the production of equipment by manufacturers worldwide. These standards do not hinder innovative design or applications but ensure efficient operation of equipment through satellites and fixed earth stations, enabling access to telecommunications networks. Pre-operational services began in the Atlantic Ocean in 1989 and will expand to the Pacific later this year. This allows users and manufacturers to test the system worldwide before it is globally commercially available. The Standard-C facilities include two methods for message storage and data messaging through short bursts of data.

The trucking industry is experiencing heightened competition and increased regulation. In order to remain compliant while optimizing vehicle and driver efficiency, fleet operators must employ real-time fleet management. Thankfully, advancements in on-board

computer systems, vehicle navigation systems, personal computers, reliable mobile telecommunications, and fleet management software have made these tools more accessible and affordable for operators.

Truck owners worldwide encounter similar challenges in maximizing their vehicle's earning potential while on the road. Some countries prohibit foreign vehicles from carrying return loads, while others struggle to identify potential cargoes. However, the latter issue is being addressed in many countries through the use of cargo brokers and clearing houses. These platforms operate databases that display available cargoes and their destinations. As a result, these services are becoming increasingly important in the competitive market as many trucks are still owner-operated.

The convergence of reliable navigation and communication systems worldwide now allows truck operators to adopt real-time fleet management solutions. These solutions will greatly enhance their efficiency and profitability in the 1990s. Specifically, the introduction of mobile satellite communications will integrate the truck and office, transforming the truck into a valuable company asset.

Natural and artificial satellites both revolve around a planet, such as Earth's moon being its natural satellite. Conversely, manmade satellites also orbit Earth while offering crucial technological progress for our planet.

The orbit of a satellite is known as its path, with the point farthest from Earth called the apogee and the closest point referred to as the perigee.

Although mass production is not typical for artificial satellites, there are two exceptions: GPS satellites and Iridium satellites. These specific types of satellites are designed for their respective purposes and produced in large quantities.

Satellites necessitate specific methods of communication with Earth.

Satellites are assigned the task of collecting and sending data.

The utilization of an antenna enables the transmission of information between different Earth locations.

Effective

communication is facilitated by radio waves, as they enable the rapid and efficient transmission of information at the speed of light.

Each satellite requires data storage and analysis capabilities, along with controls for its various systems.

The telemetry tracking and control is the satellite subsystem that handles this task.The main component or core component of the satellite and its operating system is Telemetry Tracking and Control.The ground station is responsible for receiving and storing information from the satellite, as well as handling any necessary general tasks.

The three elements of Telemetry Tracking and Control are Telemetry, Tracking, and Control.

All satellites need power sources.

The cost, durability, and effectiveness are factors that should be considered.

Satellites use a considerable quantity of electricity

The potential power sources for satellites can include solar panels, batteries, nuclear power, and heat generators.

Since 1982, INMARSAT has been offering uninterrupted direct dial telephony service to the international maritime community. In February of this year, British Airways launched comparable services for planes traversing the North Atlantic. By the end of 1989, numerous airlines will provide global aeronautical data and voice services for public calls as well as airline operational needs.

After the L-band spectrum was repurposed for mobile use in October 1987, an Extraordinary session of the INMRSAT Assembly in January 1989 sanctioned further enhancements to INMRSAT's convention for land mobile communication services.

Satellite communications are now accessible to land mobile users worldwide who require coverage beyond cellular or F3R with the introduction of pre-operational Standard service.

INMARSAT is currently the only organization that offers worldwide land mobile satellite communication services. This puts them in a unique position to quickly address the needs of their users and provide services for both public

and private closed user groups. To prepare for recent advancements, INMARSAT has conducted numerous trials and demonstrations of a low-cost data and messaging service over the past year. These trials took place in East and West Europe, Australia, and North America, and confirmed that the INWRSAT Standard C system is highly reliable and suitable for land mobile use in any condition or terrain.

The following describes the elements and details of the overall communication system that meets the goals of standardization.

COMS is a compact remote site setup that includes a low-power DC computer, an INMARSAT-C radio, and an independent power system. Through the INMARSAT-C radio, messages can be exchanged between any device on the local-area network. COMS serves as a filter, discarding incorrect packets. Additionally, the INMARSAT-C radio provides access to GPS time messages, and COMS regularly transmits time packets over the local area network.

An EIA485 local area network (LAN) offers a straightforward digital communication connection to the various components of the ARCS. This LAN is known for being dependable, energy-efficient, and resistant to external noise.

The monitor and control system (MACS) is a compact package that includes a low power DC computer, collection platform, and independent power system. MACS functions by collecting hourly averaged scientific data from the DMS and utility data from the node data units. It then transmits the coded GOES data message. In case GOES is not accessible, MACS can also send the same diagnostic data via INMARSAT. Additionally, it monitors the status of the van and generates alarm messages. Moreover, MACS can gather data sets from certain instruments if the DMS is not functioning.

The data management system, known as DMs, is a

vital component of ARCS for collecting and managing data. It runs on a reliable Sun workstation and has ample tape recording capacity. All components of the DMs, including the processors, have redundant backups.

The node data units are small micro-power data collection devices that are strategically placed throughout the ARCS system as needed. These units are responsible for performing monitoring and control tasks when instructed and also triggering specific alarm messages. Each sea container houses one NDU.

COMSAT is a service provider for the INMARSAT satellite system in the United States. There are various methods through which messages can be sent to the ARCS.

(a) Transmission directly from an INMARSAT-c radio.

(b) Connecting to COMSAT through a dial-up service.

(c) COMSAT provides an internet email service.

The ARCS communication base station is a computer that can perform multiple tasks simultaneously:

(a) Observe INMARSAT message traffic.

(b) The remote sites can be controlled by sending control commands through an operator interface.

(c) Routinely dial up and gather GOES data and then transmit them to analysis sites.

(d) When emergency messages are received, send alarm announcements.

The INMARSAT C system is a worldwide satellite system that allows for two-way data communication. It is suitable for various forms of transportation and can be easily installed and transported. This system primarily handles message-based communications and has the capability to transmit any type of information that can be converted into data bits. Messages of different lengths can be sent at a rate of 600 bits per second from C terminals, with transmission frequencies ranging from 1626.5 MHz to 1645.5 MHz and receiving frequencies ranging from 1530.0 MHz to 1545.0 MHz.

INMARSAT C is accessible on all four satellites of INMARSAT, providing

coverage across all oceans through over 40 earth stations. Each region has its own Network Control Station (NCS) responsible for managing communication traffic.

All maritime systems using INMARSAT utilize two-digit codes for transmitting and receiving different types of maritime information.The INMARSAT C mobile earth station comes with a lightweight and easy-to-install compact omni-directional antenna. It can also be equipped with directional antennas that are suitable for fixed or movable installations. The primary electronics unit has a weight of approximately 3 kg. For international business travelers and field operators, there are briefcase-style terminals available that offer convenience. The network architecture is shown below.

Figure 1. Network Architecture

Some terminals have a built-in facility for message preparation and display, while others have a serial port for users to connect their own devices for data transmission and reception. The power needs of C terminals are easily met by batteries and other resources. Currently, there are over 100 approved terminal models from nearly 40 manufacturers that can be used with the C system.

The communication system utilizes a mobile earth station that is affordable and can be installed and used on any mobile platform, regardless of its type or size. The system offers two-way messaging service and data communications using a store and forward strategy. It also provides one-way position and data polling, as well as an improved group call broadcast service that can target both groups and specific geographical areas.

Both Public and Private Networks are interconnected by the system in order to offer International, Regional, or National services. The

system has the capability to connect with any terrestrial message or data network through its store and forward feature.

In order to keep costs low and accommodate a very low G/T of -23dB/k at 50 elevations, a non-stabilized, unidirectional antenna was chosen for mobile equipment. BPSK modulation is utilized, along with a relatively low EIRP requirement of l2dBw, which can be achieved using existing semiconductors in a classA’s HPA. To mitigate the effects of multi-path propagation on a low gain antenna, a highly robust modulation and coding scheme was designed. Mobile transmissions occur between 1626.5 – 1646.5 MHz and reception between 1530.0- 1545.0 MHz, with tuning increments of 5 KHz. Standard C is capable of operating across all available frequencies on INMARSAT’s existing and next generation satellites assigned for Land Mobile use. The narrow channel spacing also ensures efficient use of limited spectrum.

The system's access control and signaling protocols have been designed with flexibility, allowing it to handle future new services and applications. Additionally, the all digital design ensures the transmission medium's transparency, allowing any type of data to pass through the traffic channels.

The current INMARSAT satellites have global beams that cover approximately 1/3 of the earth's surface. To meet the design link budget, a relatively high satellite EIRP of 21dbW is utilized. The upcoming third generation satellites will feature spot beams, allowing the Standard C system to automatically detect the appropriate beam. Due to the high power requirements, the forward carriers operate in a demand assigned mode when network conditions necessitate it. Additionally, the store and forward mode ensures maximum loading of the carriers at any given time, creating a highly cost-effective service and

mode of operation.

Each Satellite Network Region is supported by an NJS that oversees central resources such as traffic channels for demand assigned operation, signaling, and traffic control. Every NJS sends out an NJS communication signal that is received by all MES's when there is no message transfer taking place. The Communication Channel is utilized to notify mobile devices waiting at the LESS, broadcast E messages, and facilitate protocol signaling packet transfer at different stages.

Each LES acts as a intermediary between the ground network and INMARSAT Standard communications and network system. The specific types of interface available at the LES are determined by the earth station operator, but Telex and E message processing must be included. Every active mobile earth station in the network region must register with the Key. The LES keeps a copy of the registered mobile earth station list, which is used to decide whether to accept or reject calls from the terrestrial network. Furthermore, the LES also stores the location of each registered mobile earth station, allowing incoming calls intended for mobile stations in a different ocean region to be redirected and not lost.

Figure 2. An example of SES.

7.1. Improved Group Calla

The INMARSAT C terminals have the ability to receive multiple address messages, also known as EGC. For each message, a specific header is included to indicate the group of mobiles it pertains to and direct it to the appropriate area. Enhanced Group Calls can be transmitted in a range of languages and alphabets.

There are two primary forms of Enhanced Group Calls:

It offers a cost-effective and efficient way to transmit maritime safety and security information to ships at sea. Typically, it is

used by various search and rescue coastguard coordination authorities. It allows for the sending of short messages to mobile devices and from mobile devices to specific regions that are approaching.

It is highly recommended to use this technology for services specializing in advertising news, reports, and any other information about roads and ports. This technology enables the simultaneous delivery of information to a virtually limitless number of pre-designated mobile terminals.

7.2. SERVICESA

The INMARSAT C system supports bidirectional messaging, allowing messages up to 32 kilo bytes in length. A mobile earth station sends messages in data packets to a land earth station via satellite. The land earth station re-assembles the message and sends it to the intended recipient through local and international telecommunications networks. Similarly, callers can also send messages to a single mobile earth station or a group of mobile earth stations in the reverse direction.

Several users of the INMARSAT C system require data from vehicles to be obtained in order to analyze automated data collection platforms at regular or irregular intervals.

Data reporting enables the transmission of 32-byte packets of information either upon request or based on pre-arranged intervals. Conversely, polling allows users to query a mobile earth station at any given time, prompting automatic transmission of the specified information.

INMARSAT C terminals can be linked to various navigation systems for a reliable and continuous 24-hour position reporting feature. The position data can be obtained from efficient earth-based systems and satellite-based positioning systems such as the global positioning system.

In case of an emergency, the alerting equipment sends a signal. This equipment is connected to Maritime INMARSAT C terminals. A distress signal is automatically created, and the

signal contains the position and additional information to be sent to a rescue coordination centre.

Most land earth stations provide internet connectivity using the INMARSAT C service.

INMARSAT C is utilized in a variety of industries including road transports fishing boats, land mobile and aeronautical military aircraft, helicopters. Additionally, it is employed by news agency members, international business travelers, individuals involved in aid collection and remote monitoring, as well as data collection.

The INMARSAT standard C system utilizes various types of channels. These channels serve multiple purposes, including direct communication from shore to ship and inter-station links for network control and monitoring between shores.

The Network co-ordination station channel is a common channel continuously transmitted by the Network co-ordination station to all Satellite earth stations in the ocean region. Satellite earth stations tune to the Network control signal common channel when they are not operating. The channel operates at 1200 symbols per second with a fixed standard frame length of 8.64s. The information is encoded at half rate convolution and interleaved on a frame-to-frame basis. Therefore, the data rate is 600 bits per second and all messages and signaling information is transferred in packet form. Each frame has a total of 639 bytes available for packets. The first packet in each frame is the board packet, followed by signaling channel descriptor packets that provide information about the usage of signaling channels associated with that TDM carrier.

The forward link is utilized by CES TDM channel during communication between CES and a satellite earth station. CES TDM has a structure similar to the Network co-ordination station common channel mentioned above, and is responsible for carrying call set up signaling shore-to-ship messages,

acknowledgement messages, and call clear down signaling. A CES can have multiple CES Time division multiplexing channels, with each channel being demand assigned by the NCS.

The Satellite earth station signaling channels associated with each forward time division multiplexing channel are received by both the network control stations and the CES. This reception is primarily for signaling purposes from the Satellite earth station to the shore stations. Access to a Satellite earth station signaling channel is achieved using a slotted ALOHA scheme algorithm. To improve this scheme, a mechanism for reserving slots in the channel has been added. If more than one Satellite earth station transmits data at the same slot, a collision occurs, which is detected by the receiving CES. In order to reduce the time it takes for a Satellite earth station to realize that its transmission was unsuccessful, a signaling channel descriptor packet in the forward time division multiplexed indicates the current status of all slots associated with that signaling channel. The timing of these slots is based on the time division multiplexed frame of 8.64s.

In one data frame, 14 slots are reserved for current generation satellites and 28 slots are allocated for future generation satellites. The transmitted information in each slot undergoes scrambling and half rate convolution encoding. The transmission rates for current and future generation satellites are 600 symbols per second and 1200 symbols per second, respectively. One slot can accommodate 120 information bits in a burst, excluding the transmitted acquisition preamble. This arrangement aims to maximize the capacity of the signaling channel.

Satellite earth stations use message channels to transmit their messages to chosen control earth stations. The signaling

channel is utilized in the call setup phase, while the message itself is sent on a specific message channel assigned by the control earth station. Satellite earth stations access the channel using time division multiple access. The destination control earth station instructs each satellite earth station to wait for the designated time to transmit. Once assigned a start time, a satellite earth station transmits its entire message without interruption. Information to be sent is formatted into fixed packets of a set size and placed into frames. Frames can have varying sizes, but each transmission uses a fixed size. A frame can hold between one and five packets, with each packet containing 127 bytes of information. Frames are scrambled, subjected to half rate convolution, and interleaved. A preamble is added before transmission. The current generation of satellites has a transmission rate of only 600 symbols, but future satellites will increase this rate to 200 symbols per second.

Control earth stations providing C services have two-way links with the network control signal within the same region. This link is utilized for transmitting announcements and Enhanced Group Calls messages from a Control earth station to the network control signal, which will be further transmitted on the network control signal common channel. Additionally, signaling is shared via this link to ensure synchronization of access to Satellite earth stations and for allocating time division multiplexed channels to Control earth stations by the network control signal. The transmission rate is 1200 bits per second, and no error correction techniques are utilized.

Each network control signal is interconnected with the other network control signals via an inter region link channel. This channel is primarily

utilized to update other regions about any registration process performed by Satellite earth stations in a specific region. This link employs automatic dial-up voice band data channels over the public switched telephone network. The operation of these links is at a speed of 600 bits per second, using CCITT V22 full duplex modems.

Customary analogue data links achieve performance specifically defined for a particular threshold value at the receiver demodulator. The link accessibility is measured as the percentage of time that this threshold value is likely to be reached. To ensure error-free decoding at the receiver, standard C utilizes the ARQ technique to re-transmit error packets. While changes in the demodulator impact only the number of re-transmissions required, they do not affect the standard quality of the received message.

In order to reduce the loading on the satellite, it is necessary to decrease the energy per message transfer transaction to a certain extent. The forward link is particularly important as reducing power here will negatively impact the demodulator receiver and increase packet error rates. This will lead to a need for more repeat packets, resulting in reduced satellite capacity utilization. Additionally, transmitting repeat packets requires extra total message energy. Furthermore, there is the drawback of increased time needed to complete the message transfer.

In order to optimize satellite capacity, it is important to adjust the power of the satellite so that the overall energy of all messages is minimized. To achieve this, a single forward TDM can be used to serve multiple satellite earth stations. By setting the power accordingly, the rate of error in packet distribution can be evenly distributed among the satellite earth station population.

The forward

error correction uses half rate convolution on all channels. This relatively short length enables the use of maximum likelihood decoding techniques, which can provide a power gain of approximately 5 dB in an un-faded link. To establish perfect performance limits, a decoder (Viterbi) is assumed to operate on three-bit soft decision samples as a baseline.

The encoder has the capability to influence a group of 14 consecutive symbols when processing a data bit, resulting in a reduced fading bandwidth compared to the actual data rate. All of these symbols can be affected by a fade. For time division multiplexing and message channels, the symbols encoded are gathered together in a block before being transmitted. They are then transmitted in a different order, which greatly impacts signal transmission. This interleaving process spreads out the transmission of the 14 symbols associated with a specific data bit across a longer period of time than the duration of the fade.

At the receiver side, the encoded symbols are de-interleaved to effectively convert long duration fades into manageable noise that the decoder can handle. The decoder is capable of handling up to 14 corrupted symbols caused by a typical fade. The redundancy in the transmitted symbol stream enables the restoration of the original data. Interleaving is not used in the burst mode signaling channel of a Satellite earth station, as the bursts are too short to have a significant impact. However, data scrambling is still applied to all channels to ensure sufficient symbol transitions for clock recovery on the demodulator side.

Each packet includes a 16-bit checksum field that is transmitted on any of the INMARSAT C channels. The packet then goes through

de-interleaving, decoding, and descrambling operations. On the receiver's end, a checksum is calculated for each packet to determine if the received packet is error-free or not.

The provided figure below displays the channel time.

Figure 3. Channel time

The characteristics of the channel environment and protocols of the Standard-C system are utilized in the simulation environment. This is necessary because conventional analysis techniques are unsuitable for evaluating system performance. As a result, various simulators have been employed extensively.

Below is a brief summary of different simulation techniques and software programs:

A software program has been developed using the TOPSIM language to examine the packet error rate in both the forward and return links. It also assesses how different channels can affect performance.

2. The software LOTUS 123 was used to analyze the impact of specific traffic loading on a network configuration. The results obtained using this software have been valuable for demonstrating the network's capacity and predicting delays in various scenarios.

The market currently does not offer any test equipment that allows the testing of demodulator functions in multi-path fading conditions. However, we have a simulator specifically designed for this purpose.

4. The HOCUS simulation language was employed to simulate the behavior of the signaling channel, offering valuable insights on the characteristics and performance of the slotted Aloha channel, as well as the slot reservation mechanism utilized.

INMARSAT conducted a series of trials at sea and on land with controlled conditions. They purchased a number of terminals to carry out these experiments. The purpose was to test the performance of the Standard-C forward channel and evaluate the overall system performance under real traffic load. Following these trials, the coast earth

station and operational TMES were subsequently implemented.