GPRS for your PDA: CompactFlash Adapter or Bluetooth Cellphone?

August 10, 2003

Earlier this year I was looking at getting GPRS connectivity for my Dell Axim and was trying to determine if I should get the Convergent CF GPRS card or a Bluetooth-capable phone with a CF Bluetooth adapter for the Axim. I was unable to find a useful comparison of the two at the time and the CF GPRS card seemed a better idea. For the benefit of those in the process of making the same decision here are some observations that may help you.

I do not find cellphone-PDA cables a convenient option; it's yet another thing to carry along and you need a new cable if you change your cellphone or PDA. This leaves the following options:

  1. If you have a non-BT cellphone and don't want to swap it for a BT-capable cellphone, your best bet is the Convergent GPRS card. The card is approx $250 and if you want to make voice calls and/or send and receive SMS messages you will also need add-on software like Running Voice GSM or connect2Internet PRO, approx $30. In addition you will also need a SIM card and service and the charges depend on the provider.
    • The data-only plans of most operators are targeted at business users and are expensive for casual users.
    • Another option is to get new service on the PDA (voice and data) and use the voice software for making calls and SMS. T-Mobile has been offering unlimited GPRS for $19.99 on top of a voice plan of $29.99 or higher. The CF card is quite usable for making calls and SMS communication but not very convenient to receive calls; you have to keep the PDA on at all times. Running Voice GSM does has an option to turn the screen off and you can salvage some battery life. It looks like my 2215 can last an entire day in this mode. The only drawback is that you will need to use the headset for voice calls. The PDA's mic and speaker are not supported.
  2. If your cellphone is BT-capable but your PDA is not, option 1 might still be a good bet. I have no experience with Bluetooth CF or SD cards but if you're going to have to carry another card you might as well get the GPRS card. However option 1 requires new service, so for those that want a cheaper alternative, get a BT card and go for option 3.
  3. This option is for those that have a BT-capable PDA and a BT-capable cellphone. It is the least expensive from a service standpoint because you only need to add data service to your existing cellphone service. If you're already a T-Mobile subscriber unlimited GPRS service is only $19.99 extra. I also find this option the most convenient if your PDA has BT built-in. No extra cards to carry around, no swapping CF cards or SIM cards, etc. I also expected to get better life on the PDA because the BT link to the cellphone requries less power than the GRPS link to the cellular base station. In unscientific measurements I found the CF GPRS card required 25% more power. [Unscientific because the measurements were based on looking at the battery meter after 30 mins of download tests.]

Both the Cellphone/BT and CF GPRS options are comparable in performance, although in my tests the T68i-Bluetooth link was somewhat faster. The tests were conducted within a one hour interval using my iPAQ 2215 on T-Mobile's GPRS network in a location with good signal strength.

 

Convergentech Card
with PPC 2003 drivers

Convergentech Card
with Flexport drivers

Sony Ericsson T68i + Bluetooth

Average time to connect

16s

16s

10-12 seconds
(BT association in 2-4s)

Download speed for 50 kB block

39 kb/s

41 kb/s

52 kb/s

Download speed for 200 kB block

20 kb/s

32 kb/s

27 kb/s

 

The Flexport drivers are installed with Running Voice GSM software which includes a graphing utility that displays the downlink data rate in real-time. The graphs helped explain why 200kB downloads were slower than 50 kB downloads in my tests; the data rate dropped to almost zero at times and dragged the average down.

In conclusion the option that works best for you depends on your current service and hardware inventory and also how much you are willing to invest in new hardware and service charges. I chose option 1 at the onset because my PDA at the time lacked built-in Bluetooth and I had no GSM service. Sometime later I signed up with T-Mobile and made sure my cellphone had Bluetooth capability ($150 for the SE T68i on eBay, unlocked for $15 at a local store). I recently switched to the iPAQ 2215 and since then option 3 has been the better solution.