IEEE DySPAN Part #2
On our YouTube channel, you can now find some short videos of the software-defined radio, cognitive radio and dynamic spectrum access demonstrations and trials by the participants at the IEEE DySPAN 2007 conference held in Dublin last April. Motorola Labs, Shared Spectrum Company, SRI International, University of Kansas, Virginia Tech, and Anritsu are featured in addition to CTVR groups from Ireland. A short overview of this year’s conference can also be found below. We will continue to add videos to this as they arrive. Huge thanks to Kate McKeon for taking care of the camera work and sitting through hours of footage to come up with these.
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Testing wireless broadband on the move
The opinions expressed here are the author’s only and do not necessarily represent those of CTVR.
We have finally got around to trying out one of the Huawei 3G wireless broadband modems. These are white mouse-like USB devices that operators including Vodafone, O2 and 3 are marketing at the moment in a bid to capture revenue from those who want internet connectivity on the move or simply want an alternative to dial-up but cannot, for one reason or another, use wireline broadband. These little white devices all come from the same manufacturer however the operator logos, price plans and basestation networks differ.
Our model is the Huawei E220 high-speed downlink packet access (HSPDA), which claims a top speed of 3.6Mbps. The nice thing about this is that it is powered from the USB port and contains all the software needed to get going; it’s advertised as an autoinstall procedure but it can take a bit of prodding to install correctly. Normally, USB ports can supply up to 0.5A when requested. The modem package we received included a two-USB to single cable connector enabling the modem to be powered from two USB ports. This can be very handy because sometimes USB ports can fail to deliver enough current to keep power-hungry devices happy.
Of course, the actual download speed is dictated by the number of concurrent users per basestation sector. For non-HSPDA-enabled basestations, the connection falls back to general packet radio services (GPRS), which has a top rate of 236.8kbps. A quick speed test in the front square of Trinity College Dublin resulted in 2.6MB/s…perhaps the operator was watching. On a daily return train journey from Mullingar, Co. Westmeath to Dublin city, the unit switched between UMTS and GPRS and handed over between basestations fairly well. It is still not as seamless as one might like; the connection was dropped several times as it switched between HSPDA and GPRS. The lowest reported rate experienced when connected to a non-3g enable basestation in Mullingar was marginally over 53kB/sec Despite these issues, it is proving very handy for getting through part of the daily barrage of emails before getting into the office. On the evening train, the problems are more to do with the lack of elbow movement on the packed train rather than technological ones.
3 Ireland and Vodafone charge for exceeding a usage cap (which includes both uploads and downloads) whereas O2 currently employ a ‘fair usage’ policy. This makes better sense for the rare occasions when the cap may be exceeded (if you are lucky enough to enjoy a good and consistent rate).
O2 Ireland have three 5MHz UMTS frequency division duplexing (FDD) paired carriers, or spectrum segments, and one 5MHz UMTS time division duplexing (TDD) unpaired carrier. The downlinks from the basestations occur in the frequency range from 2155MHz to 2170 MHz. The uplinks from the modem use the frequency range between 1965MHz-1980MHz. We decided to take a closer look at what goes on behind the scenes in the modem, specifically by taking a look at the physical random access channel (PRACH), which is used to transmit the random access channel (RACH) preamble. Upon start-up, this is the first transmission from the modem as it attempts to find and connect to, a basestation.
Using an Anritsu MS2781A Signature spectrum analyser, we were able to locate the specific uplink frequency used by the modem. We then placed the modem close to the antenna connected to the analyser. A zero-span trace of the estimated centre frequency of the uplink channel, which was triggered when the detected power exceeded the noise floor of the system, allowed us to capture the following time-domain plot of the random access channel transmissions.
This shows a series of pseudo-random QPSK bursts (preambles) of 1ms duration gradually increasing in power until the power is sufficient enough to enable a basestation to receive it. What is impressive is that when the basestation finally detects the modem, it replies and the modem begins transmitting a longer connection message all within about a 4ms period.
For latency-intolerant applications e.g. some on-line multiplayer games, this would not the best solution, however a couple of short Skype calls of acceptable quality were experienced. For this operator at least, P2P client operation was possible.
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Matt Ettus – Ettus Research and GNU Radio is coming to town
Matt Ettus of Ettus Research and the open-source GNU radio project will be presenting some of his work and talking about the GNU Radio project on Wednesday August 1st in CTVR’s HQ, Lloyd Institute, Trinity College Dublin.
Matt is one of the lead people working on the GNU Radio project. His expertise spans the software and hardware areas directly related to the areas of software-defined radio and dynamic spectrum access. He developed the universal software radio peripheral (USRP), pronounced usurp, and daughterboards, which we have been using as our RF frontends to develop our experimental systems, and for the recent tests and trials of dynamic spectrum access technologies.
GNU Radio is a collection of software that when combined with minimal hardware, allows the construction of radios where the actual waveforms transmitted and received are defined by software. The project is very active with many contributors from academic, industrial and commercial backgrounds.
Date: Wednesday August 1st
Time: 2.30pm
Room: 1.07
Lloyd Institute
Trinity College Dublin
Email us at enwireless at ctvr.ie if you would like to attend.
Directions to the Lloyd Institute
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Tomdependence Day
Tom Rondeau from the Center for Wireless Telecommunications, part of the Wireless @ Virginia Tech group has joined us for a year. We are very excited about this because it allows us to really get moving on some highly interesting cognitive radio and dynamic spectrum access ideas and projects under development at the moment. Paul and Keith spent some time over with Tom in VT last year and between them (and lots of really good coffee), successfully demonstrated coexistence (the ability of two or more different services to operate on a common centre frequency, and in the same location) and interoperability between CTVR’s reconfigurable radio platform and GNU Radio’s open source software radio system for the first time. We reported some of the early results of this work at this year’s CCNC conference in Las Vegas and IEEE DySPAN conference in Dublin.
Naturally, we chose July 4th to welcome Tom to CTVR and Ireland properly; a day we named Tomdependence Day in his honor.
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Measuring spectrum usage across Ireland
In May of this year CTVR held a plenary meeting in Ennis, Co. Clare on Ireland’s west coast. CTVR researchers travelled from each of the eight centre locations around the country. Members of the Emerging Networks (EN) strand, based in University of Dublin, Trinity College, travelled across the country from Dublin, which is on the east coast.
Taking advantage of this opportunity, Keith, Deepak and Paul from the EN strand commandeered the CTVR radio van and, using an Anritsu MS2781A signal analyzer coupled to a few sturdy laptops, measured spectrum occupancy along their route across the country.
Some of these results and their route according to the recorded GPS waypoints can be found on the EN webpages here.
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Measuring spectrum usage in Dublin
As well as demonstrating the neXt Generation XG nodes, Shared Spectrum Company set up their spectrum monitoring station on top of ComReg’s HQ in Dublin with superb help from ComReg’s team during the IEEE DySPAN conference in April. Shared Spectrum Company has carried out a similar set of measurements in New York City and Washington DC and it was the first time they had ventured to Europe to carry out a similar set of measurements.
For approximately 40 hours, the wireless activity in Dublin city, from 30MHz up to 3000MHz was measured using their state of the art monitoring equipment
More photographs can be found here
The measurements show how spectrum usage varies between day and night. In some frequency bands, no spectrum usage was detected (at this location anyway). In others, especially in the case of the mobile phone, analogue and digital terrestrial TV (DTT), and digital audio broadcasting (DAB), frequency spectrum is in continuous use. The intermittent use of frequency spectrum is especially apparent in the UHF personal mobile radio (PMR) bands. The frequency-sweeping characteristics of radar signals can be observed in the 2686 to 2900MHz range. On some channels, the RF power from the antenna was almost -10dBm, probably due to high power transmissions from Three Rock mountain, which is visible from this location. The 88-108MHz frequency range was blocked to avoid desensitising the monitoring equipment due to the extremely high power in this band.
A brief report and plots of Shared Spectrum Company’s measurements in Dublin can be downloaded as a zip file here
Alternatively, Shared Spectrum Company’s spectrum measurement plots can be viewed here:
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Sculpting spectrum with reconfigurable OFDM
We have just posted a video on our YouTube channel showing our reconfigurable OFDM system in action. In this example, we are transmitting at 2.35GHz using a bandwidth of 1MHz. We have a test licence from ComReg under their innovative Wireless Test and Trial scheme for cognitive radio & dynamic spectrum access testing within a 25MHz band centred at this frequency in addition to another 25MHz centered at 2.08GHz.
In this case, the FFT size is 256 and the number of subcarriers is varied from 255 (full-bandwidth), right down to zero, in both contiguous and non-contiguous configurations. We are using one of the Universal Software Radio Peripherals (USRPs) by Ettus Research LLC
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IEEE DySPAN Part #1
The 2007 IEEE Symposium on New Frontiers in Dynamic Spectrum Access Networks (DySPAN) was held in Dublin this April. We hosted a series of trials and demonstrations involving dynamic spectrum access and cognitive radio technology using a trial licence issued by ComReg
QinetiQ, Shared Spectrum Company, Motorola, SRI International, Virginia Tech and Kansas University were among those taking part in a collaborative attempt to see the latest dynamic spectrum access technology in action using both licenced and licence-exempt spectrum.
It was a valuable and enjoyable experience for all as it was the first time all of these groups were in the same place and delegates could see the latest technologies up close rather than just reading about them in a publication.
On the Saturday before the conference, Shared Spectrum Company conducted a trial of two XG nodes operating in the same DySPAN trial channels as QiniteQ’s HAVE QUICK radios.
On Monday and Tuesday, the conference venue became a ‘hack-fest’ where just about all of the demonstrators spent their time tweaking, debugging and developing their systems even further.
More info at the DySPAN demonstrations webpage
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