10 posts by 7 authors in: Forums > CWNA - Enterprise Wi-Fi Admin
Last Post: August 22, 2011:
  • hi

    i need some advice and solution. my friend have a food court and want to offer internet access to its customer and buyers.

    i need to know that hardware and software will be more appropriate.. (AP,PoE switch, Server ..etc)

    its must comprise of prepaid ticket etc..or any other ways of authentication or payment method

    we need to have full control and statistics also


    ashley from Mauritius

  • well nearly 80 views and no one was able to help me...

    am i really on the good site ;)..

    Plz anyone ..any advice is acceptable..u can PM me also



  • Hi Ashley,

    My gut feeling based on the lack of response is that hotspot services is like asking how long is piece of string :-). There are many many ways to do it. I ain't no expert but here are some tutorial that may assist you. All retrieved from google search:

    1) Easy overview of HotSpot

    2) DDWRT HotSpot building tutorial

    For DDWRT, best to ask the DDWRT forum for any assistance. I don't think here is the right forum to ask.

    Keep those question coming. I'll try and support the fellow "oversea" users. I also live in an island but its huge. It's called Australia :-)


  • I recently saw some information from Aruba on the Amigopod. I think it would really fit your needs well. I know it will give you a basic skinning ability so you can make the splash screen your own, as well as having the ability to do authentication etc. I don't work for Aruba, but I was pretty impressed with the offering. Anyway I hope that helps. I know it's not the full info, but I hope it at least gets you going in the right direction.

  • Brad,

    Amigopod is a brilliant skinning platform for hotspots. Entire McDonald in Australia uses Amigopod. I also don't work for Aruba but I can see why Aruba recently acquired Amigopod. Great buy!.

    I believe they can also do some location based advertising but this isn't based on RFID it uses the individual AP to provide which clients are connected to the AP. So AP#1 which is near the pizza hut store, can generate relevant advertising splash to the users connected in that region. It's very simple but a lot more cost effective then the usual wifi based RFID solution.

  • Hi,

    I am studying for CWTS and I don't get what packet binary convolutional code (PBCC) is and

    how OFDM(orthogonal frequency division multiplexing) works.

    The only thing I know about OFDM is that it has multiple channels so that data can go through each channel

    in parallel.

    Please help...

  • For The CWTS exam, it is highly unlikely that you will be asked any detailed questions on PBCC or OFDM.

    Radio links, in general ( not just Wi-Fi ) operate via a noisy medium. Depending upon the frequency and type of radio involved, galactic noise ( from radio stars ), atmospheric noise, noise from electric motors, fluorescent lights etc, may have an effect on the quality of the signal. Depending upon the severity of the noise/interference, the signal quality may drop down to such a low level, that the receiver is unable to properly interpret the data received, and an error ( or errors ) is/are indicated.

    In the early days of High Frequency or HF radio, ( 3 ? 30 MHz ), if a block of data was received corrupted, the receiver could request a retransmission of that block of data by sending an ?ARQ? or Automatic Repeat Request code to the transmitter. The transmitter in turn, would repeat the data sent previously. Hopefully, this retransmitted block would be received correctly. If not, the process would be repeated.

    When satellite communications began, utilizing geostationary satellites operating at approximately 22,300 miles above the earth?s surface, a new problem arose. Due to the finite amount of time required for a signal to travel from the transmitting earth station to the receiving earth station ( depending upon the physical location on the earth?s surface of both stations relative to the satellite ), this method became impractical. It takes approximately a quarter of a second ( roughly ) for a signal to go from the transmitting earth station, to the satellite and down to the receiving earth station, for it to be received ( with errors in this case ), and for the receiving earth station to send an ARQ code back up to the satellite and then back down to the original transmitting earth station. This delay made the ARQ technique impractical for this type of communication.

    A new series of error detecting and correcting codes were devised to allow a transmitting earth station to send a signal to a receiving earth station, and for that station to not only detect any errors, but to correct them as well ( with a high probability of success?..error detection and correction does not work perfectly 100% of the time ). Convolutional codes were devised in which the output of the encoder depended upon previous inputs, hence ?convolution? occurred. Dr Andrew Viterbi ( of Qualcomm fame ) developed a receive decoding system using the Viterbi algorithm ( utilizing soft decision decoding ). Very often, the convolutional encoder would work with it?s corresponding Viterbi decoder. Since then, a number of coding/decoding schemes have appeared on the scene, including Reed-Solomon, Turbo etc.

    By means of using Error Detection and Correcting codes ( EDC ), the receiving earth station would no longer need to send an ARQ signal to the transmitting station, as it was capable of performing both error detection and correction at it?s own end, thus negating the need for a delay inducing transmission to the original earth station which sent the message.

    One of the advantages of OFDM is that there are a number of sub-carriers, and if a realtively narrow ( bandwidth wise ) amount of interference is received, it may still be possible to reconstruct the original information without severe loss.

    The theory behind both can be quite involved.


  • I sometimes think of OFDM as being similar to packet switching technology. Would that be true?

  • [quote]I sometimes think of OFDM as being similar to packet switching technology. Would that be true?[/quote]

    OFDM is somewhat like cable TV. One wire, many radio channels

    But it does not carry the shopping channel and the all Gilligan channel. You put in a high speed digital signal, it gets distributed across the many radio channels, transmitted, received, demodulated and reassembled into one high speed digital signal

  • One of the things that surprises many people is to find that the RF modulated signal which carries digital data is not itself a digital signal. Many books refer to the ?RF digital signal?. It has now become commonplace to use that term, although it is not technically correct.

    Whether transmitting an analog ( like an FM radio signal for example ) signal or a digital signal, the actual modulated RF signal itself is not digital but rather analog. For those reading through the CWDP book, there are many references to the I and Q diagrams and constellation diagrams. These are man-made entities that help us to visualize what is ?going on ? within the radio signal. When a transition occurs from a zero to a one in BPSK for example, the carrier signal ?sweeps through? a large range of frequencies on both sides of the carrier. In BPSK diagrams, we see nice clean carriers at zero and 180 degrees. However, in ?moving from one phase to another? a whole range of frequencies are present. It is extremely difficult to explain this with anything other than some high-level signal theory.

    OFDM helps solve a problem that is present in all radio channels?..frequency selective impairments. This simply means that at different times ( down to the microsecond ), the radio channel environment can vary, as people move around, air temperature changes occur, vehicles move around etc. This means that different frequencies are affected more or less at different times. OFDM has a sort of ?built in redundancy? whereby the data to be transmitted is ?spread around?.but not like spread spectrum? a number of ?mini-channels? within one actual physical Wi-Fi channel. Through some clever electronics and processing, OFDM signals can ?take a hit? on a number of those ?mini-channels?, and in many instances may be able to reconstruct the original message. The ?mini-channels or subcarrier channels ? which are affected can change according to interference and changes in the radio environment.

    The data which is input to an OFDM system has many different processes applied to it, but essentially the data is broken up into a number of blocks. These blocks are used to individually modulate each mini-channel. The mini-channels are all ?combined together? and transmitted.

    The CWNA book gives some good basic information on OFDM. It?s another one of those areas like antenna theory where you can only go so far in understanding it?s operation before some detailed math is required.

    Packet switching technology occurs at the baseband level, i.e. before modulation.

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