Introduction
The 802.11 based dual-band system is a full duplex system utilizing a very well known standard, IEEE 802.11 OFDM based technology based on the IEEE released draft. This system is identical to previous MDSA designed systems except for the usage of custom modulators in the MVDDS bands and demodulators in both bands. In order to reduce complexity, we used well known mass marketed Atheros chipsets as our modulation engines. A cascade combiner arrangement allows for almost plug and play scalability.
The system operates in a Point to Multipoint to Multipoint distribution arrangement. This arrangement uses a central site, the Network Operations Center, which is connected to the Internet IP backbone at high bandwidth. It also has 4 large dedicated lines to a provider NOC where linear video content resides. These links enable the remote billing and SMS services. This NOC is connected by Point-to Point-Microwave links to MVDDS distribution towers and reception base-station nests.
The downlink of this system is in KU-band occupying 12.2 to 12.7 GHz. A MVDDS tower will employee multiple sectors, each sector capable of full spectral usage in both polarizations. A typical tower is usually 2 sectors to start and at maximum capacity could grow to 6 sectors. MDSA has engineered this system to reach 5 mile distribution of 16QAM (3/4 FEC) modulated signal at 14dBm per 24 MHz with a path budget that accounts for rain fade by more than 6 dBm.
The sectors will use 20 MHz channels with 50 active transponders. One transponder will be held as redundant in case of failure. The channels used are 20 MHz wide OFDM modulated (802.11) channels with 802.11 channel masks. This will result in 43 Mbps per channel.
The uplink is in the frequency range of 5.725-5.825 GHz range. This allows for an output power of 4 watts.
The 802.11 technology used is flexible in both modulation schemes and channel width. This is one of the most widely utilized wireless standards. The table below shows the supported modulation schemes:
| Modulation | Modulator bandwidth using 20 MHz Channels |
| QPSK 3/4 | 21.7 Mbps |
| QAM 16 (16QAM) 1/2 | 28.9 Mbps |
| QAM 16 (16QAM) 3/4 | 43.3 Mbps |
| QAM 64 (64QAM) 3/4 | 65 Mbps |
The above modulation types are adaptively (increasing with signal quality) encoded and sent over an OFDM-256 inside the 20 MHz channels being used in up-link and the same for down link channels.
The system uses OFDM based 802.11standards to implement basic fixed wireless point to multipoint service.
The system operates in FDD mode with the following channel size combinations:
1. 20 MHz Downling, 20 MHz uplink.
Platform and Architecture
DownLink
The downlink to subscriber's CPE is up converted to 12.2 GHz to 12.7 GHz from L-Band at the modulators.
CH1 12.2 to 12.220 CH2 12.221 to 12.141 CH3.......
UpLink
The uplink from subscribers uses long range point to multi-point 802.11 base stations as reception basestations. These will operate at one per channel per sector with a typical cell using 4 sectors of 4 channels for a total of 16 20 MHZ channels used across 4 sectors. This is to insure non interference with other users of the 5.7 GHz band.
CH1 802.11 (1) CH1 802.11 (2) CH1 802.11 (1) CH1 802.11 (2)
CH1 802.11 (3) CH1 802.11 (8) CH1 802.11 (3) CH1 802.11 (8)
CH3 802.11 (6) CH3 802.11 (10) CH3 802.11 (6) CH3 802.11 (10)
CH3 802.11 (12) CH3 802.11 (18) CH3 802.11 (12) CH3 802.11 (18)
The receive base stations are mounted on towers with clearance from any buildings of at least 50 meters to clear it form any multi-path reflections from buildings. Backhaul can be done over free to air 5 GHz links. These base stations have very low power draw and are unobtrusive. Each base station can serve 1000 customers. Particular attention is paid to the multiplexing of these customers.
Asymmetric Routing
The data component of the system will operate in Asymmetric IP routing mode. This will allow automatic provisioning of the customer and will include support for DHCP on the Customer Premise Equipment, CPE’s and a DHCP server on the Base station to avoid fixed IP addresses. The connection of the upstream and down streamside of this system is accomplished at the IP layer. This means that the downstream Ku band radio signal can be received from a location that is distinct from the upstream reception base station. This allows for more flexibility in coverage planning.
This means that the linking of the upstream to the downstream is done on the IP layer and not on the RF layer. This allows the downstream transmission location and the upstream reception location to be diverse. All towers and 5.8 GHz PPTs will be linked back to a MVDDS tower or the NOC by wireless backhaul in the 5.8, 11, 18, or 34 GHz bands. This allows for very high-speed transfer of data and video across the entire network.
IP TV Delivery
MDSA’s challenge was to deliver large amounts of high bandwidth television without saturating available data bandwidth. Today's home are outfitted with more than one television capable of HD video display.
MDSA solved this problem by modulating carriers of linear digital television as IP data receive only streams that are available at all times to the Set top box. Since the modulators are independent of each other they can all be turned to individual IP TV carriers. As they are also independent of the data modulator, the usage of any or all of the three receive only demodulators will not affect the data bandwidth throughput.
Including the receive-only SoCs, the MDSA CPE is theoretically capable of delivering 288 Mbps of data to the individual user. In reality, delivery of 3 HDTV signals and high-speed data access is effortless for this design. As the most watched channels are multicast, the number of simultaneous viewers of these channels will not affect the throughput AT ALL.
The customer will be able to dedicate as many transponders as the situation requires for dedicated video. Three channels in these dedicated streams will be available to the user. In theory, these receive only channels could be opened to provide higher speed data downlinks (100+ Mbps) for a specific user.
Downlink spectrum allocation will be in the 12.2 – 12.7 GHz band. MDSA uses optimized frequency channel widths for Video and Data broadcast measuring 20 to 27MHz to insure harmonious coexistence with regional DBS operators.
Functional overview
Video applicationThe received television programs at the NOC are provided as IP data. Groups of these channels are routed to a modulator where the modulator will package it and send it out as a transport stream using an address receivable by all CPEs on the sector.
This transport stream is decoded by the CPE and Set Top box user’s desired linear television data stream is isolated. All other data from this transport stream is discarded. The desired channel is routed to the Set Top box box for display on the television.
This is achieved by a MDSA modulator design utilizing 602.11 chipsets on a custom programed, single board computer with an integrated 5.7 GHz radio. Each one of these modulators are capable of modulating one 20 MHz wide transport stream. These are designed to CARRIER GRADE specs with built in redundant power supplies.
The RF output of these boards are down converted to L-Band and cascade - combined into the Wide band Ku-Band transmitters. This removes the traditional DVB-S (Q-8PSK) modulator from the systems and replaces it with a modulator of much greater spectral efficiency. All non video-dedicated transport streams are available for IP data delivery. In addition, an over the air antenna is installed at the time of installation for connection to the Set Top box for local television reception.