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Buriedcode
Joined: 06 May 2004
Posts: 341
Helped: 36
Location: London
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 24 Dec 2005 16:31 2.4 ghz dsss |
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Hi,
I'm trying to design a wireless media system, and I'm really not up to designing the RF from scratch. I've got a couple of analogue 2.4Ghz module for experimenting with different pulse shaping methods, SNR etc.. and a few 2.4Ghz FHSS IC's, that I'm making a dev board for. I'm sure both of these will be adequate for my needs (up to 5Mb/s), and the FHSS system would help with avoiding interference a great deal.
But, just for my own comparison, has anyone ever seen OEM modules that use DSSS? I'm not talking about 'Zigbee' modules, even though these use DSSS, they just don't have the throughput I need (I think they run from 62.5kb/s to 250kb/s).
I'm not suggesting a pre-built wi-fi card, just the RF part without the PCI interface. I can't afford an FPGA for all the filtering, pulse shaping and spreading code, so I was hoping that there are some nice little OEM modules that do it all for me, letting me worry about the protocol/data etc.. Idealy running at a minimum of 1.5Mb/s.
That way I can compare DSSS and FHSS in different situations and whether its suitable for my system. I know I sohuld probably build it from scratch, and I'm sure i could, but as I said, its terribly complex, and expensive. Out-sourcing the RF part is the only way..
Thanks, and Merry Christmas,
BuriedCode.
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pisoiu
Joined: 31 Dec 2002
Posts: 702
Helped: 25
Location: Romania
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24 Dec 2005 17:17 2.4ghz dsss |
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Perhaps Nordic (www.nvlsi.no) will suit your needs. You have some options, you can use nRF2401A and build the protocol youself, using direct mode (data rate 1Mbps), or you can use nRF24E1, which also includes an 8051 modified CPU (Synopsys DW8051 core). With the CPU included, you can only use the ShockBurst mode, which is a form of protocol already built, meaning you don't have to worry about preamble CRC and packet addressing, but this mode have some drawbacks. You can send only 256 bits at a time.Also, mode change (RX/TX) , parameters programming (channel no.) will take some time, so the average data rate is not 1Mbps. However it is easy to use, it worth a look.
/pisoiu
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Buriedcode
Joined: 06 May 2004
Posts: 341
Helped: 36
Location: London
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24 Dec 2005 19:50 dsss module |
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Hi,
pisoiu, thankyou for your reply!
I will definately look into it. I cannot reduce my datarate much, but at a push, 1mb/s might be possible. As far as switching modes, its basically a one-way system, although it'll be nice to have the option of feedback from the receiver. I'm 'fairly' sure that I can handle the protocol myself (preamble, data encoding, FEC etc...) so I'll go with the chip.
Cheers for your help,
BuriedCode
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pisoiu
Joined: 31 Dec 2002
Posts: 702
Helped: 25
Location: Romania
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25 Dec 2005 2:41 2.4ghz digital audio modules |
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Search the forum for "nRF" , "nordic" etc or after my posts, hopefully you will find some helpfull hints about it, especially about the RF part, where there are some more informations than in the datasheet. I've used this chip (nRF24E1) extensively, and I will hapily answer to your questions.
/pisoiu
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25 Dec 2005 2:41 Ads |
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zolam
Joined: 03 Oct 2005
Posts: 94
Helped: 9
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29 Dec 2005 17:17 2,4 ghz fhss ic |
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| check philips site i saw there something interesting
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Buriedcode
Joined: 06 May 2004
Posts: 341
Helped: 36
Location: London
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31 Dec 2005 21:49 que signifie 2.4 ghz dsss |
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hi agian,
Zolam, I checked the philips website...
They've got a new 2-chip system for wireless digital audio....looks very promising. Its narrow band for the 868/900 ISM band and uses SBC compression, which is very similar to the latest bluetooth audio links. Also, low letency.
Although my design can't use compression (really harsh restrictions on quality and latency of >4ms, my own restrictions, but I must abide  ) I will see if I can get a sample, for testing. I think it can be configured to bypass the compression.
Thanks all for the input. It's good to know people have used different systems, and not all promoting one manufacturer.
BuriedCode.
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DonJ
Joined: 27 Dec 2004
Posts: 123
Helped: 2
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11 Jan 2006 22:58 dsss module |
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Not so many chips can support 1.5 Mbps.
Nordic Semiconductor is a good start.
Good hunt!
A.T.B.
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Buriedcode
Joined: 06 May 2004
Posts: 341
Helped: 36
Location: London
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12 Jan 2006 19:32 2.4ghz dsss |
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hi again,
| Quote: |
| Not so many chips can support 1.5 Mbps. |
Tell me about it! Thats why I was hoping for some Wifi-like system. Since DSSS is direct spreading, generally the bandwidth of these is 11-22Mhz. A nice DPSK 2-5MB system would do. I've even thought about buying a cheap wireless network card, and ripping out the baseband IC, leaving the screened RF circuit with on-board antenna's, and all the analogue....In fact...I often use pre-built computer parts, since they're so cheap and easily available...eg: old SDRAM is cheaper than the individual chips, and you get about 5.
anyway, the hunt continues.....
Thanks,
BuriedCode.
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