问题出在这个无线网卡驱动的参数为省电节能模式，信号强度不行。需要修改参数来重启下wifi，就可以了。
首先输入lspci查看你的无线网卡驱动。
00:00.0 Host bridge: Intel Corporation Haswell-ULT DRAM Controller (rev 09)
00:02.0 VGA compatible controller: Intel Corporation Haswell-ULT Integrated Graphics Controller (rev 09)
00:03.0 Audio device: Intel Corporation Haswell-ULT HD Audio Controller (rev 09)
00:14.0 USB controller: Intel Corporation 8 Series USB xHCI HC (rev 04)
00:16.0 Communication controller: Intel Corporation 8 Series HECI #0 (rev 04)
00:1b.0 Audio device: Intel Corporation 8 Series HD Audio Controller (rev 04)
00:1c.0 PCI bridge: Intel Corporation 8 Series PCI Express Root Port 1 (rev e4)
00:1c.2 PCI bridge: Intel Corporation 8 Series PCI Express Root Port 3 (rev e4)
00:1c.3 PCI bridge: Intel Corporation 8 Series PCI Express Root Port 4 (rev e4)
00:1c.4 PCI bridge: Intel Corporation 8 Series PCI Express Root Port 5 (rev e4)
00:1d.0 USB controller: Intel Corporation 8 Series USB EHCI #1 (rev 04)
00:1f.0 ISA bridge: Intel Corporation 8 Series LPC Controller (rev 04)
00:1f.2 SATA controller: Intel Corporation 8 Series SATA Controller 1 [AHCI mode] (rev 04)
00:1f.3 SMBus: Intel Corporation 8 Series SMBus Controller (rev 04)
02:00.0 Network controller: Intel Corporation Wireless 7260 (rev 73)
03:00.0 Unassigned class [ff00]: Realtek Semiconductor Co., Ltd. Device 5287 (rev 01)
03:00.1 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 12)
04:00.0 3D controller: NVIDIA Corporation GK107M [GeForce GT 750M] (rev a1)
看到倒数第四行是无线网卡信息：02:00.0 Network controller: Intel Corporation Wireless 7260 (rev 73)，型号为Intel的7260。
再来查看7260这块网卡驱动的参数信息，iwlwifi其实就是Intel® Wireless WiFi driver for Linux。
输入modinfo iwlwifi查看网卡驱动参数信息。
name: iwlwifi
vermagic: 4.13.0-38-generic SMP mod_unload
parm: swcrypto:using crypto in software (default 0 [hardware]) (int)
parm: 11n_disable:disable 11n functionality, bitmap: 1: full, 2: disable agg TX, 4: disable agg RX, 8 enable agg TX (uint)
parm: amsdu_size:amsdu size 0: 12K for multi Rx queue devices, 4K for other devices 1:4K 2:8K 3:12K (default 0) (int)
parm: fw_restart:restart firmware in case of error (default true) (bool)
parm: antenna_coupling:specify antenna coupling in dB (default: 0 dB) (int)
parm: nvm_file:NVM file name (charp)
parm: d0i3_disable:disable d0i3 functionality (default: Y) (bool)
parm: lar_disable:disable LAR functionality (default: N) (bool)
parm: uapsd_disable:disable U-APSD functionality bitmap 1: BSS 2: P2P Client (default: 3) (uint)
parm: bt_coex_active:enable wifi/bt co-exist (default: enable) (bool)
parm: led_mode:0=system default, 1=On(RF On)/Off(RF Off), 2=blinking, 3=Off (default: 0) (int)
parm: power_save:enable WiFi power management (default: disable) (bool)
parm: power_level:default power save level (range from 1 - 5, default: 1) (int)
parm: fw_monitor:firmware monitor - to debug FW (default: false - needs lots of memory) (bool)
parm: d0i3_timeout:Timeout to D0i3 entry when idle (ms) (uint)
parm: disable_11ac:Disable VHT capabilities (default: false) (bool)
可以看到倒数第五行这个参数power_save:enable用来控制节能的，里面默认default: disable是关闭的，但是这里不知道为什么变成开启了，所以我们需要给它改回去。
首先我们把配置驱动的文件打开sudo vim /etc/modprobe.d/iwlwifi.conf。
按i进入编辑模式，在下面一行添加参数options iwlwifi power_save=0。
按ESC后输入：wq保存配置文件后,运行如下命令来重启应用，更新wifi配置信息。
sudo modprobe -r iwlwifi
sudo modprobe iwlwifi
当然嫌麻烦直接重启也是可以的。