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Modifying your Download Patterns Based on the Connectivity Type

When it comes to impact on battery life, not all connection types are created equal. Not only does the Wi-Fi radio use significantly less battery than its wireless radio counterparts, but the radios used in different wireless radio technologies have different battery implications.

Use Wi-Fi

In most cases a Wi-Fi radio will offer greater bandwidth at a significantly lower battery cost. As a result, you should endeavor to perform data transfers when connected over Wi-Fi whenever possible.

You can use a broadcast receiver to listen for connectivity changes that indicate when a Wi-Fi connection has been established to execute significant downloads, preempt scheduled updates, and potentially even temporarily increase the frequency of regular updates as described in Optimizing Battery Life lesson Determining and Monitoring the Connectivity Status.

Use Greater Bandwidth to Download More Data Less Often

When connected over a wireless radio, higher bandwidth generally comes at the price of higher battery cost. Meaning that LTE typically consumes more energy than 3G, which is in turn more expensive than 2G.

This means that while the underlying radio state machine varies based on the radio technology, generally speaking the relative battery impact of the state change tail-time is greater for higher bandwidth radios.

At the same time, the higher bandwidth means you can prefetch more aggressively, downloading more data over the same time. Perhaps less intuitively, because the tail-time battery cost is relatively higher, it's also more efficient to keep the radio active for longer periods during each transfer session to reduce the frequency of updates.

For example, if an LTE radio has double the bandwidth and double the energy cost of 3G, you should download 4 times as much data during each session—or potentially as much as 10mb. When downloading this much data, it's important to consider the effect of your prefetching on the available local storage and flush your prefetch cache regularly.

You can use the connectivity manager to determine the active wireless radio, and modify your prefetching routines accordingly:

ConnectivityManager cm =
 (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);

TelephonyManager tm =
  (TelephonyManager)getSystemService(Context.TELEPHONY_SERVICE);

NetworkInfo activeNetwork = cm.getActiveNetworkInfo();

int PrefetchCacheSize = DEFAULT_PREFETCH_CACHE;

switch (activeNetwork.getType()) {
  case (ConnectivityManager.TYPE_WIFI):
    PrefetchCacheSize = MAX_PREFETCH_CACHE; break;
  case (ConnectivityManager.TYPE_MOBILE): {
    switch (tm.getNetworkType()) {
      case (TelephonyManager.NETWORK_TYPE_LTE |
            TelephonyManager.NETWORK_TYPE_HSPAP):
        PrefetchCacheSize *= 4;
        break;
      case (TelephonyManager.NETWORK_TYPE_EDGE |
            TelephonyManager.NETWORK_TYPE_GPRS):
        PrefetchCacheSize /= 2;
        break;
      default: break;
    }
    break;
  }
  default: break;
}
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