WO2003009494A1

WO2003009494A1 - Ground-to-satellite-to-aircraft communication system

Info

Publication number: WO2003009494A1
Application number: PCT/IL2002/000576
Authority: WO
Inventors: Dov Zahavi; David Mansour; Avi Meidan; Yitshak Shemer; Simha Erlich
Original assignee: Elbit Systems Ltd.
Priority date: 2001-07-18
Filing date: 2002-07-16
Publication date: 2003-01-30
Also published as: IL144420A0

Abstract

As part of the present invention there is a satellite base station for communicating with a mobile communication unit such as an aircraft. The satellite base station may include a modem functionally associated with an up converter and a down converter, a power amplifier to receive and amplify an output of the up converter, and a controller unit functionally associated with the modem and said amplifier. The controller may be adapted to adjust the power gain or the data rate of the base station based on a signal received from the mobile communication unit.

Description

Ground-to-Satellite-to-Aircraft Communication System

Field of Invention

The present invention relates in general to satellite-to-air communication and specifically to broadband satellite-to-aircraft communication and control.

Background of the Invention

Although airborne communication services, including the Internet, have improved during the last decade, they still do not offer the range of options available in land-based communication. One of the main obstacles restraining airborne communications is limited bandwidth.

Until the advent of widespread use of the Internet and mobile communications, phenomena of the last decade or so, airborne systems did not need to address the problem of limited bandwidth. The main users of aircraft-to-ground (via satellite) communications were pilots and ground crew. The bandwidth requirements were limited (in comparison to recent requirements), and communication priorities were well defined.

Typically, the problems of aircraft-to-ground/ground-to-aircraft communication were addressed by narrow-band communication solutions (e.g. satellite communication systems, such as Inmarsat). However, these solutions are not appropriate for bandwidth intensive communications, such as airborne Internet and mobile communications. Such solutions are not cost effective, nor do they optimize bandwidth use.

Furthermore, one of the main issues challenging satellite communication is high operating costs due to, among other reasons, limited resources. A typical satellite communication system assigns a uniform usage level for all airplanes and does not consider the real usage of each platform. It is thus not always very cost effective.

Summary of the Invention

There is therefore provided, in accordance with an embodiment of the present invention, a communication system. The communication system may include one or more airborne systems, a satellite, a base station and a satellite controller. The satellite controller may be in communication with the airborne systems and the satellite. According to their bandwidth requirements, the satellite controller may be adapted to control the communication between the satellite and the airborne systems. The satellite controller may supply data from a content provider.

The satellite controller may be part of the communication system or an independent element adaptable for use in other systems.

Furthermore, according to some embodiments of the present invention the communication system may include one or more airlines and one or more airline controllers. Each airline may include one or more aircrafts. Each of the airline controllers may be associated with each of the airlines, for prioritizing communication patterns of each of the one or more aircrafts. The patterns may be identified according to data relevant to each aircraft ( e.g. - By the use of IP addresses ). The data associated with each aircraft may be, for example, priority data or quality of service data. Other aircraft associated data may be used.

According to a further embodiment of the present invention the communication system may include one or more airborne systems, one or more satellites, and one or more regional controllers. Each satellite may be adapted to communicate with a designated area, for example each satellite may be adapted to communicate with an area that is substantially correlated to the coverage area of that satellite. The regional controllers may be capable of communicating with the airborne systems and the satellites, and may be adapted to switch communications between two or more of the satellites when one or more of predefined criteria are met, for example, the regional controller may switch the communications from a first satellite having a first designated area to a second satellite having a second designated area, when the airborne systems move from the designated area of the first satellite to the designated area of the second satellite, such that a substantially continuous communication may be achieved. The communication system may further include a satellite controller associated with each satellite.

Moreover, according to an embodiment of the present invention, the communication system may include one or more regional controllers, one or more airline controllers, and one or more global centers. The regional controllers may be adapted to determine a satellite-to-aircraft communication link. The airline controllers may be adapted to prioritize communication between one or more aircrafts of an airline. The global centers may be in communication with the regional controllers and the airline controllers, and may process data functions associated with the one or more aircrafts and the one or more regional controllers.

According to another embodiment of the present invention, the communication system may include one or more airborne systems, and one or more ground systems. Each of the ground systems may be in communication with the airborne systems. Each of the ground systems may be adapted to control the allocation of bandwidth to each of the airborne systems associated with it. The communication system may also include one or more satellites. Each of the satellites may be in communication with one or more airborne systems and one or more ground systems. Each of the ground systems may include a satellite controller such as that described above.

In addition, according to another embodiment of the present invention, each of the airborne systems may include one or more of the following: an onboard system controller, an antenna, a ground system, a content provider, and a transceiver. The antenna may be in communication with the onboard system controller, a ground system and a content provider. The transceiver may be adapted to supply data to the ground system in connection with the bandwidth usage of the airborne system.

Brief Description of the Drawings

The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the appended drawings in which:

Fig. 1 is a block diagram of a communication system, operated and constructed according to an embodiment of the present invention;

Fig. 2 is a block diagram of a ground satellite controller used in the communication system of Fig. 1 , operated and constructed according to an embodiment of the present invention;

Fig. 3 is an airborne communication system used in the communication system of Fig. 1 , operated and constructed according to an embodiment of the present invention.

Fig. 4 is a block diagram of a communication system, operated and constructed according to an embodiment of the present invention; and

Fig. 5 is a graph of power consumption for several airborne platforms and usable in the communication system of Fig. 4.

It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. Detailed Description of the Present Invention

The present invention is an airborne communication system that utilizes wide-band, two-way communication and provides connection between a content provider and an onboard system. According to an embodiment of the present invention the communication system may be a satellite communication system capable of utilizing a protocol for implementing bandwidth control, for example, by means of power and bit-rate control per each user. Communication via one satellite transponder may be optimized by means of the protocol described therein.

Furthermore, the present communication system may be based on

SATCOM using Ku geo-synchronous satellites. The existing coverage by Ku geo-synchronous satellites may be sufficient to provide two-way, wide-band data communication to aircraft on most commercial airlines. The solution may provide a broadband communication system that can support multiple users.

Fig. 1 is a block diagram of a communication system 10, operated and constructed according to an embodiment of the present invention. System 10 may comprise one or more satellite controllers 20, one or more regional controllers 12, one or more global centers 16 and one or more airline controllers 18, wherein typically each airline controller 18 may be dedicated to an associated commercial airline. Typically, each satellite controller 20 may be coupled to a dedicated ground satellite station 23 and antenna 22.

Via one or more satellites 14, communication system 10 may provide connection between a content provider and an onboard system 40. The number of satellites 14 used in system 10 may depend, for example, on the selected coverage range, in one embodiment of the present invention, each satellite 14 may be associated with one dedicated controller 20. For example, if Intelsat #603 is used for covering Western Europe, then a dedicated controller 20 may be used to control the communication via this satellite transponder.

Generally, a regional controller 12 may be used for route control, for example, for the Pacific Route. Regional controller 12 may connect all satellite controllers 20 that are covering the assigned region. Regional controller 12 may monitor the availability of regional satellites and correlate optimal bandwidth usage.

The tasks of regional controller 12 may include managing the table of satellite availability, coordinating satellite swaps, collecting billing data from the ground stations, calculating satellite availability according to regional traffic, monitoring satellite availability, and communicating with the content provider, the global center 16 and other regional controllers 12.

Since the connection of onboard system 40 to the content provider may be typically via regional controller 12, it may be possible to avoid disconnection when moving from one satellite to another. In addition, when moving from one region to another, (i.e. from Europe to the United States), the connection to the content provider may be maintained through the same regional controller 12. The use of the regional controllers 12 may allow the communication session to continue when the communication system shifts from one satellite to another thus, avoiding disconnection over the Atlantic.

Usually, only one global center 16 may be used to correlate and coordinate world-wide activities of system 10 and to interface with airline controllers 18.

The tasks of global center 16 may include collecting billing data (world-wide) and producing bills. Global center 16 may also collect load and capacity information, collect fault information and analyze collected information for service improvements. Global center 16 may collect information on satellite resource usage for payment to suppliers, receive flight schedules from the airline controller 18, and receive from the company controllers information on departures and arrivals. Global center 16 may also send join/cut-off requests, which may be according to the airlines' schedules, to regional controller 12.

Airline controller 18 may monitor the activities of its associated airlines, including aircraft-user privileges and other commercial airline activities (e.g. landing and take off times, the number of airborne aircrafts, etc.) and may inform global center 16 of data such as updated departures/arrivals.

One of the advantages of system 10 may be the ability to combine new system controllers with an existing satellite infrastructure, i.e. the system may use existing satellite stations and attach to them the new controllers 20.

Reference is now made to Fig. 2, a block diagram of the elements of satellite controller 20. Satellite controller 20 may comprise a ground satellite controller 24, and a receiver/transmitter (Rx/Tx) module 26. Rx/Tx module 26 may comprise a transmitter 27 and a receiver 28.

It is noted that in Fig. 2 satellite controller 20 is illustrated adjacent to, and in communication with, an existing satellite station 23 comprising antenna 22. However other arrangements and configuration may be used.

Transmitter 27 comprises a modem 27A and an up converter 27B. Modem 27A may be of the type described in Israeli Patent Application "A Multi-Mode Modem for Use in Satellite Communication Systems", assigned to the same assignees and filed herewith. Transmitter 27 may allow the transfer of data in different rates, according for example to such factors as the bandwidth required by the aircraft or the reception conditions at the aircraft's receiver. Transmitter 27 may be adapted to transmit the total data rate using simultaneous sub-channels, such that, for example each sub-channel uses a fraction of the total data rate. Each sub-channel may be associated with an orthogonal spread sequence. Transmitter 27 may also implement an Error Correction Code and may allow the transmission of different power levels over each of the sub-channels, thereby increasing bandwidth usage.

Receiver 28 may comprise a modem 28A and a down converter 28B. Per each time frame, receiver 28 may adapted to report to the ground controller the power level of the received signal . This information may allow the ground controller 24 to evaluate the signal power required for each aircraft.

Satellite controller 20 may monitor the movement of an aircraft in the respective satellite region and communicate with regional controller 12. Satellite controller 20 may also initiate join processes and cut-off processes for aircraft entering and exiting the satellite coverage area. Satellite controller 20 may implement the communication regime, i.e. it may receive the content provider data and prepare it for an uplink channel. Satellite controller 20 may also receive a downlink channel and prepare it for the ISP. Typically, satellite controller 20 may control the efficient power allocation for each aircraft, verify privileges of served aircraft (user priority, applications launched, etc.) and may calculate sun direction relative to each aircraft.

Satellite controller 20 may also request satellite swap in case of sun blinding or in case of poor coverage by the currently used satellite. Satellite controller 20 may also be used to track services for billing (at the level of both the airline and the end user).

Reference is now made to Fig. 3, a block diagram of onboard

system 40 used in the communication system of Fig. 1 , operated and

constructed according to an embodiment of the present invention.

Onboard system 40 may provide a generally optimal solution for bringing

broadband data to an existing onboard communication network server 42.

Onboard system 40 may comprise an onboard system controller 44, an antenna controller 52, a Rx Tx module 46 coupled to an antenna 48. The Rx/Tx module 46 may comprise one or more receivers 54 and transmitters 56.

Each receiver 54 may include a receive modem 54A and a down converter 54B. Each transmitter 56 may include a transmit modem 56 and an up converter 56B. Modems 54A and 56A may be of the type described in Israeli

Patent Application "A Modem for use in Communication Systems", assigned to the same assignees and filed herewith.

Onboard system 40 may connect to onboard communication network server 42, which may be adapted to provide connection to passenger seat (i.e.: laptop) 50. Onboard system controller 44 may initiate and implement join processes and cut-off processes, transmit and receive data to the Internet Server, and obtain navigation data from the aircraft via a data bus. Onboard system controller 44 may connect to and manage antenna controller 52 and Rx /Tx module 46. Onboard system controller 44 may request satellite resources from the ground controller, implement a communication regime, prepare data to send to the ground, receive ISP data from the ground, perform satellite swap processes and perform Doppler calculations.

Antenna controller 52 may couple to and control a transmission antenna 58 and a reception antenna 60. Typically antennas 58 and 60 may be high speed electronically controlled antennas. Antenna controller 52 may receive aircraft location and attitude data from onboard system controller 44 and may receive satellite direction information and power, polarization, and frequency requirements from satellite controller 20. Antenna controller 52 may directly control the antenna according to the required performance.

Transmitter modem 56A may be adapted to implement error correction code, data compression and data security according to the control received. Receiver modem 54A may be adapted to de-spread one or more orthogonal sequences that may be associated with sub-channels transmitted by the ground transmitter. Receiver modem 54A may also be adapted to implement error correction codes and data security and report the power level of the signal received in each time frame to onboard system controller 44. This may allow onboard system controller 44 to incorporate the received signal power level into the control data transmitted to the satellite controller 20, and the ground controller 24 may then decide whether to increase or decrease the power for a given aircraft.

Following are descriptions of exemplary processes using system 10. To facilitate understanding, refer again to Figs. 1 and 3.

Net-Join Log On

Airline controller 18 may send a departure message to global center 16 in correlation with an aircraft departure. The message includes aircraft identification (secret code), source and destination.

Global center 16 may be adapted to calculate the region of departure and may send a message to the regional controller 12 with the joining data.

Regional controller 12 may be adapted to calculate which satellite 14 may be used for the communication and may send a message to the satellite controller 20 with the joining data. Regional controller 12 may also send the data from the selected satellite to global center 16.

Global center 16 may be adapted to send the data from the selected satellite 14 to airline controller 18, which may be adapted to send the data to the aircraft.

Data correlated with a selected satellite 14 may be entered into onboard system 40 (i.e. the communication frequency is set).

Satellite controller 20 may be adapted to send an initiate message to the aircraft. Onboard system controller 44 may be adapted to direct antenna 48 to the selected satellite 14 and may wait for the init message to arrive. When onboard system controller 44 may receive an initiate message, it may send back to satellite controller 20 a response including the identification code.

Satellite controller 20 may wait for a response from the aircraft. When the response from the aircraft arrives, satellite controller 20 may check the identification code. If it is a valid code, the join process may be completed. If not, a rejection message may be sent to the aircraft.

On a periodic basis, the status of the join process may be sent to both regional controller 12 and global center 16.

Log-off

Onboard system controller 44 may be adapted to ensure that all users have logged off. Onboard system controller 44 may be adapted to send a cut-off message to satellite controller 20. When satellite controller 20 receives a cut-off request, it may reconfirm it with the aircraft.

The aircraft may be adapted to send a confirmation message and may stop the transmission. Satellite controller 20 may update tables of satellite resources and may stop the transmission.

Satellite switching

For ease in identification, please note: The current satellite controller 20 is the controller currently in use, which is to be disconnected to the system. The new satellite controller 20 may the controller to be joined to the system. The old satellite controller 20 may be the controller that has been disconnected.

The regional controller 12 may be adapted to identify the need to switch satellite 14. Regional controller 12 may find a new satellite 14 in its region that can provide the connection. Regional controller 12 may be adapted to notify the current satellite controller 20 to send the data identifying new satellite 14 to onboard system controller 44. Onboard system controller 44 may confirm reception, and may set a timer.

Regional controller 12 may be adapted to instruct the new satellite controller 20 to send an init message. Once the timer expires, onboard system controller 44 may direct the antenna to the new satellite 14 and may attempt to receive the init message.

If the onboard system controller 44 fails to receive the init message within

TBD time, it may return communication to the old satellite 14 and notify the old satellite controller 20 of the failure.

If the onboard system controller 44 fails to receive the init message, it may send an init message response together with the identification code to the new satellite controller 20.

The new satellite controller 20 may identify the aircraft and move to normal mode. Onboard system controller 44 may also move to normal mode.

The new satellite controller 20 may be adapted to communicate with the content provider via regional controller 12, for example, after experiencing a short disconnection (the recovery is typically taken care of by the content provider). The old satellite controller 20 may update tables of satellite resources and may stop the transmission both to the aircraft and to regional controller 12.

When the two satellites are in different regions the content provider, which is connected to a regional controller 12, may not changed.

Regional Controller and Satellite switching

For ease in identification, please note: The current regional controller 12 is the controller currently in use, which is to be disconnected from the system. The new regional controller 12 is the controller to be joined to the system. The old regional controller 12 is the controller that has been disconnected.

The current regional controller 12 may identify a need to switch satellites but may fail to locate a suitable new satellite 14 in its region. The current regional controller 12 may notify global center 16 about the need to find a new satellite 14 in another region.

Global center 16 may identify a suitable satellite 14 in a neighboring region. It may then send the current regional controller 12 the data corresponding to the new regional controller 12 (from the area of the suitable satellite 14). The current regional controller 12 may commence communication with the new regional controller 12.

The current regional controller 12 may notify the current satellite controller 20 to send the new satellite 14 data to onboard system controller 44. Onboard system controller 44 may confirm reception and may set a timer.

The current regional controller 12 via the new regional controller 12 may notify the new satellite controller 20 to send init messages.

Once the timer has expired, onboard system controller 44 may direct antenna 48 to the new satellite 14, and wait for the init message.

If onboard system controller 44 fails to receive the init message within TBD time, it may return to the old satellite 14 channel and notify the old satellite controller 20 about the failure. If onboard system controller 44 fails to receive the init message, it may send an init response with the identification code to the new satellite controller 20.

The new satellite Controller 20 may identify the aircraft, and may switch move to normal mode. Onboard system controller 44 may also switch to normal mode.

The new satellite controller 20 may communicate with the content provider via the new regional controller 12, which may communicate with the old regional controller 12, after experiencing a short disconnection.

The old satellite controller 20 may update tables of satellite resources, and may stop the transmission both to the aircraft and to the old regional controller 12.

Communication Performance

Fig 4. is a block diagram of a system 70 that may be adapted to provide a solution to the communication bottleneck typically found in the satellite communication (SATCOM) link portion of a general communications system in accordance with an embodiment of the present invention. System 70 may monitor power requirements by various airborne platforms 76, and may be adapted adjust bandwidth thereto accordingly.

System 70 may include a base station 72, a satellite 74 and one or more airborne platform, generally designated 76. The system in accordance with an embodiment of the present invention may provide a connection, generally

designated 78, for connecting the base station 72 and the satellite transponder

74. For ease of understanding, the communication link from base station 72 to

satellite 74 is designated connection 78', and the communication link from

satellite 74 to base station 72 is designated connection 78".

Furthermore, the connection between satellite 74 and each platform 76

may be an associated connection, generally designated 80. For ease of

understanding, the outbound communication (uplink) from satellite 74 to each associated platform 76 is designated connection 80', and the inbound

communication (downlink) from each associated platform 76 to satellite 74 is designated connection 80".

Base station 72 and each platform 76 may include a modem/receiver/

transmitter unit 82 and a control computer 74.

System 70 may be adapted to constantly monitor reception parameters at

each of the platform 76 (e.g. signal strength) and adjust accordingly the

number of sub-channels and the power of each of sub-channel of connection 80

that may be dedicated to the associated platform 76. It is assumed that typically

the land line portion of the system 70 have sufficient margin to accommodate

requirements.

Uplink connection 78' and 80' may carry data from base station 72, via

satellite 74, to the platforms 76. The reception conditions at each of the platforms 76 may be determined by a set of predetermined factors, for example

the following factors may be used: Effective Isotropic Radiated Power ( EIRP ) of the satellite at the location

of the aircraft. This may be strong when the aircraft is located close to the

footprint center and decreases when the aircraft approaches margins. The EIRP

may be a given factor in the system and apart from changing the used satellite,

the system should make best use of EIRP distribution in real time as a function

of the service requirements of aircraft competing for bandwidth from the same

transponder.

Receiver antenna gain over temperature (G/T) on board the aircraft. This

is a measure of the antenna effectiveness in utilization of the available satellite

EIRP. G/T may be determined by two factors:

Antenna gain towards the satellites. This is a direct derivative of antenna

area projection on a plane perpendicular to the line of sight from the aircraft to

the satellite. It should be noted that antenna gain is also a function of

polarization which changes with the satellite and the aircraft location, and also

with the change of attitude of the aircraft, relative to the line of sight to the

satellite.

Receiver sensitivity may be determined by the first stage amplifier technology and by the antenna design and installation to minimize thermal

noise.

The allocation strategy arbitrates between the different platform 76

competing for bandwidth. The system may efficiently utilize the resources as

they become available.

The communication on the uplink connection 78' and 80' may be based on a wide variety of communication protocols, for example DVB-S protocol. Typically, each platform or group of platforms 76 may have a dedicated frequency band, as designated by connections 80A', 80B' and 80C. The frequency band may be defined, for example, in accordance with the platform location in the satellite coverage area.

Downlink connection 78" and 80" may transmit data from the platforms 76 via satellite 74 to base station 72. Bandwidth may be limited by the EIRP of the transmit antenna aboard the platform 76. Another factor here may be avoidance of interference to other satellites and network management of all inbound traffic to minimize interference between platform 76. Other factors may also be taken into consideration.

The downlink connection 78" and 80" may use a dedicated frequency band for each platform 76, as designated by connections 80A", 80B" and 80C". To avoid inter satellites interference various know solutions may be used, for example, spread spectrum may be used on the Tx from the Platform 76.

System 70 may also be used to monitor and regulate the power for each platform 19. The platforms 76 in the best satellite coverage area may use lower power consumption than the platform 76 near the boundaries of the satellite coverage area. Additional factors affecting power consumption may be the number of users and/or software applications utilized by each platform 76; such that the more bandwidth required, the more power required for transmitting the data. A third parameter that may influence the power consumption may be the privileges of the users in the platform 76, ( i.e. first class vs. economy class, the prime minister's aircraft vs. regular airline, etc.). Other parameters may also influence the power required for transmitting the data.

For power control implementation, the modem unit 82 may monitor, in

every time frame, the power of the signal received from satellite 74. The modem

unit 82 may report the status to its associated controller 84, which may then

report the information to base station 72. Station 72 may collect the data from

each platform 76 that uses a specific satellite 74 and may evaluate the power

requirements of each one of the platforms 76. A platform 76 that reports low

receiving power, may be allocated a higher transmitting power from the ground

station, and vice versa.

Base station 72 may consider all needs of platform 76, including the

parameters mentioned above, and decide the power regime of which platform

76 receives more or less power, accordingly.

Reference is now made to Fig. 5, which is a schematic diagram of the communication and power regime for three platforms 76A - C under the same

coverage from a single satellite 74, in a given time frame in accordance with an

embodiment of the present invention.

The platform 76A may be adapted to use a relatively narrow bandwidth, while platforms 76B and 76C may be adapted use variable bandwidth

consumption.

Platform 76B may be launched with a high bandwidth consuming

application, and thus may receive high power transmission. Platform 76C may

be launched with a low bandwidth consuming application, and thus it may receive low power transmission. The whole available bandwidth may be split between both platforms, thus both platforms 76B and 76C may receive medium resources. When the platform 76B switches off the high consuming application, the platform 76C may receive more power resources for itself.

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims that follow:

Claims

1. A satellite base station for communicating with a mobile

communication unit, said satellite base station comprising:

a modem functionally associated with an up converter and a down

converter,

a power amplifier to receive and amplify an output of said up

converter; and

a controller unit functionally associated with said modem and said

amplifier, said controller adapted to adjust a transmission characteristic of

said base station based on a signal received from said mobile

communication unit.

2. The satellite base station according to claim 1 , wherein said controller

unit is adapted to adjust said power amplifier's gain.

3. The satellite base station according to claim 1 , wherein said controller

unit is adapted to adjust said modem's data rate.

4. The satellite base station according to claim 1 , wherein said modem is a spread spectrum modem and is adapted to spread data associated

with a specific mobile communication unit using at least one spreading

sequence.

The satellite base station according to claim 4, wherein said controller

unit is adapted to either add or remove a spreading sequence used by

said modem for a given mobile communication system.

The satellite base station according to claim 5, wherein said controller

unit is adapted to instruct said modem to partition data for a given

mobile communication unit into data segments and to spread at least

two data segments using different spreading sequences.

7. The satellite base station according to claim 5, wherein said controller

unit is adapted to instruct said modem to use two or more spreading sequences for data for a given mobile communication unit using.

8. A method of communicating through a satellite base station with a

mobile communication unit, said method comprising:

receiving a signal indicating reception conditions at the mobile communication unit; and

adjusting a transmission characteristic of said base station based on

the signal received from said mobile communication unit.

The method according to claim 8, wherein the transmission characteristic of said base station is adjusted by adjusting a gain of an

associated power amplifier.

10. The method according to claim 8, wherein the transmission

characteristic of said base station is adjusted by adjusting an

associated modem.

11. The method according to claim 10, wherein adjusting the modem

comprises adjusting the modem's data rate.

12. The method according to claim 10, further comprising spreading data

associated with a specific mobile communication unit using at least one spreading sequence.

13. The method according to claim 12, wherein a spreading sequence is

either added or removed from a set of spreading sequences used by

the modem for a given mobile communication system.

14. The method according to claim 13, comprising partitioning data for a

given mobile communication unit into data segments and spreading at least two data segments using different spreading sequences.

15. The method according to claim 13, comprising using two or more

spreading sequences for the same data relating to a given mobile communication unit using.

16. A mobile communication unit for communicating with a satellite base

station, said unit comprising:

a modem functionally associated with an up converter and a down

converter, and

a controller unit functionally associated with said modem and said

amplifier, said controller unit is adapted to send to the base station a

signal correlated to a desired received signal characteristic.

17. The mobile communication unit according to claim 16, wherein the

desired received signal characteristic is signal strength.

18. The mobile communication unit according to claim 16, wherein the desired received signal characteristic is data rate.

19. The mobile communication unit according to claim 16, wherein said

modem is a spread spectrum modem and is adapted to de-spread data associated with received signal using at least one spreading

sequence.

20. The mobile communication unit according to claim 19, wherein said controller unit is adapted to either add or remove a spreading sequence used by said modem.

21. The mobile communication unit according to claim 21 , wherein said controller unit is adapted to instruct said modem to partition received data into data segments and to de-spread at least two data segments using different spreading sequences.

22. The mobile communication unit according to claim 21 , wherein said controller unit is adapted to instruct said modem to use two or more spreading sequences for the same received data.