1page.title=Modifying your Download Patterns Based on the Connectivity Type
2parent.title=Transferring Data Without Draining the Battery
3parent.link=index.html
4
5trainingnavtop=true
6previous.title=Redundant Downloads are Redundant
7previous.link=redundant_redundant.html
8
9@jd:body
10
11<div id="tb-wrapper">
12<div id="tb">
13
14<h2>This lesson teaches you to</h2>
15<ol>
16  <li><a href="#WiFi">Use Wi-Fi</a></li>
17  <li><a href="#Bandwidth">Use greater bandwidth to download more data less often</a></li>
18</ol>
19
20<h2>You should also read</h2>
21<ul>
22  <li><a href="{@docRoot}training/monitoring-device-state/index.html">Optimizing Battery Life</a></li>
23</ul>
24
25</div>
26</div>
27
28<p>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.</p>
29
30<h2 id="WiFi">Use Wi-Fi</h2>
31
32<p>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.</p>
33
34<p>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 <a href="{@docRoot}training/monitoring-device-state/index.html">Optimizing Battery Life</a> lesson <a href="{@docRoot}training/monitoring-device-state/connectivity-monitoring.html">Determining and Monitoring the Connectivity Status</a>.</p>
35
36<h2 id="Bandwidth">Use Greater Bandwidth to Download More Data Less Often</h2>
37
38<p>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.</p>
39
40<p>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.</p>
41
42<p>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.</p>
43
44<p>For example, if an LTE radio is has double the bandwidth and double the energy cost of 3G, you should download 4 times as much data during each session&mdash;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.</p>
45
46<p>You can use the connectivity manager to determine the active wireless radio, and modify your prefetching routines accordingly:</p>
47
48<pre>ConnectivityManager cm =
49 (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);
50
51TelephonyManager tm =
52  (TelephonyManager)getSystemService(Context.TELEPHONY_SERVICE);
53
54NetworkInfo activeNetwork = cm.getActiveNetworkInfo();
55
56int PrefetchCacheSize = DEFAULT_PREFETCH_CACHE;
57
58switch (activeNetwork.getType()) {
59  case (ConnectivityManager.TYPE_WIFI):
60    PrefetchCacheSize = MAX_PREFETCH_CACHE; break;
61  case (ConnectivityManager.TYPE_MOBILE): {
62    switch (tm.getNetworkType()) {
63      case (TelephonyManager.NETWORK_TYPE_LTE |
64            TelephonyManager.NETWORK_TYPE_HSPAP):
65        PrefetchCacheSize *= 4;
66        break;
67      case (TelephonyManager.NETWORK_TYPE_EDGE |
68            TelephonyManager.NETWORK_TYPE_GPRS):
69        PrefetchCacheSize /= 2;
70        break;
71      default: break;
72    }
73    break;
74  }
75  default: break;
76}</pre>