DirectBand
DirectBand is a North American wireless datacast network owned and operated by Microsoft. It uses FM radio broadcasts in over 100 cities to constantly transmit data to a variety of devices, including portable GPS devices, wristwatches and home weather stations.
How it works
DirectBand uses the 67.65 kHz subcarrier leased by Microsoft from commercial radio broadcasters. This subcarrier delivers about 12 kbit/s (net after ECC) of data per tower, for over 100 MB per day per city. Data includes traffic, sports, weather, stocks, news, movie times, calendar appointments, and local time.
Not like RDS
DirectBand does not use the RDS (Radio Data System) subcarrier. RDS is a different system and has much lower data rate (~730 bit/s after ECC, including framing). Its much narrower subcarrier is primarily used for radio station information and traffic. DirectBand and RDS can co-exist on the same FM station.
Forward Acting Error Correction
Since many DirectBand uses are mobile, and there is no opportunity to request retransmission of a broadcast signal, DirectBand utilizes an advanced error-correction strategy that allows for reconstruction of messages even when sizable portions of the message are lost due to buildings, tunnels or other obstructions of the FM signal. Error correction is 1/2 rate interleaved trellis with time diversity, soft-decision decode. The DirectBand data rate is in excess of 12 kbit/s after ECC.
Push network
DirectBand is a push network—new content is delivered every 2 minutes. Users pre-select the virtual channels that they are interested in.
Receivers
There are a variety of DirectBand receivers. All use a small (2.794 mm x 2.794 mm x 860 µm) radio receiver. Some designs add an ARM7-based processor.
The initial DirectBand products were a series of data watches. These had mild success, but never met expectations and production of new watches was discontinued in 2008. Recently, several other applications have surfaced, the most visible being the traffic data/local info market, particularly to auto GPS sets for Garmin and Avis. This competes directly with older RDS-based services, which operate at a substantially lower data rate.
Microsoft design
DirectBand is a product of the Smart Personal Objects Technology (SPOT) team at Microsoft. System hardware was designed for Microsoft by SCA Data Systems of Santa Monica, CA.[1] MSN Direct is the consumer brand that Microsoft uses for devices that receive content from the DirectBand network.
FM subcarrier usage
RDS uses a portion of the FM station spectrum immediately above the stereo signal, centered at 3x19 kHz (the stereo pilot frequency). RDS extends between about 55 and 59 kHz. DirectBand is above RDS, extending from about 59 kHz to 75 kHz.
Future
On October 26, 2009, Microsoft announced that MSN Direct service would end on January 1, 2012.[2]
Although this clearly indicates Microsoft's intent to cease usage of the service, it is not yet known whether the DirectBand technology will be sold to another company, such as one of the hardware licensees of MSN Direct (e.g. Garmin) -- or whether the technology will be put in the public domain as an open source technology.
See also
- RDS
- PSIP
- Error correction
- Modem
- FM broadcasting
References
- ↑ SCA Data website
- ↑ "MSN Direct service will be available only until January 1, 2012. publisher=MSN Direct web site".
External links
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